Should fix #22226.

Code introduced in #20890 caused a regression that broke color flooding animations in a BottomNavigationBar that has BottomNavigationBarType.shifting.

The original issue (#19653) dealt with background color changes not occurring until another tab was selected. The result is that the background color instantly changes whenever the state changes and when the widget changes, instead of allowing a new widget to animate the background color change.

When converting all of the samples to use the snippet tool, I encountered some bugs/shortcomings:

1. The document production took 90 minutes, since the snippet tool was being invoked from the command line each time. I fixed this by snapshotting the executable before running, so it's down to 7 minutes.

2. The sample code was not being properly escaped by the snippet tool, so generics were causing issues in the HTML output. It is now quoted.

3. Code examples that used languages other than Dart were not supported. Anything that highlight.js was compiled for dartdoc with is now supported.

4. The comment color for highlight.js was light grey on white, which was pretty unreadable. It's now dark green and bold.

https://github.com/flutter/engine/compare/824daacf6d95...e64af7510e89

git log 824daacf6d95..e64af7510e89 --no-merges --oneline
e64af7510 Roll src/third_party/skia 2a13921745eb..67f5c0ceac22 (2 commits) (flutter/engine#6777)


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https://github.com/flutter/engine/compare/4f4c470d2419...824daacf6d95

git log 4f4c470d2419..824daacf6d95 --no-merges --oneline
824daacf6 Roll src/third_party/skia 3daed9b12db4..2a13921745eb (1 commits) (flutter/engine#6776)


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* early return for initialRoute + test

https://github.com/flutter/engine/compare/e61f05256eaa...4f4c470d2419

git log e61f05256eaa..4f4c470d2419 --no-merges --oneline
4f4c470d2 Roll src/third_party/skia 630e7d651a34..3daed9b12db4 (6 commits) (flutter/engine#6775)
177e043b5 fix setInitialRoute (flutter/engine#6774)
6fa5c0a82 Pass scriptCode into Locale on initialization. (flutter/engine#6711)

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https://github.com/flutter/engine/compare/dda667f8f093...e61f05256eaa

git log dda667f8f093..e61f05256eaa --no-merges --oneline
e61f05256 Roll src/third_party/skia 2aa9a22fe159..630e7d651a34 (5 commits) (flutter/engine#6773)
21eb1caae Update the contributing guide (flutter/engine#6754)

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dda667f8f Roll update to harfbuzz to 2.1.0 (#6760)
e8f0c08c9 Add instructions to download the full license log diff. (#6771)
5077e95f1 Roll src/third_party/skia f2b35e4fb8cc..2aa9a22fe159 (7 commits) (#6770)

* Improves error message and adds test.

5006ce574 fix type in embedded views preview flag name (flutter/engine#6767)
eec27fc8a Roll src/third_party/skia e70c6b13dd55..f2b35e4fb8cc (6 commits) (flutter/engine#6768)
aea7071e2 Roll src/third_party/skia e6c85755832b..e70c6b13dd55 (1 commits) (flutter/engine#6766)
1132d6c42 Roll src/third_party/skia 11407e56f277..e6c85755832b (2 commits) (flutter/engine#6765)

This reverts commit 71e9bd6f.

* add an analysis_options excludes for the build/ dir

* fix bots

https://github.com/flutter/engine/compare/3374f4cce045...fb5b097e5c20

git log 3374f4cce045..fb5b097e5c20 --no-merges --oneline
fb5b097e5 Revert "Roll freetype2 to a10b062df0c8958d69377aa04ea6554a9961a111 (#6738)" (flutter/engine#6763)
4fd2d1486 Roll src/third_party/skia 5b2bda70e52f..11407e56f277 (1 commits) (flutter/engine#6762)
fa4c01ee6 Add an Info.plist flag to enable the embedded iOS views preview. (flutter/engine#6756)
ded297f59 Roll src/third_party/skia df8225e253a2..5b2bda70e52f (5 commits) (flutter/engine#6761)
f0380b397 Roll src/third_party/skia 32262da42bed..df8225e253a2 (10 commits) (flutter/engine#6755)
124f20f40 Clear the on-screen surface every frame. (flutter/engine#6753)

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https://github.com/flutter/engine/compare/b5758d0d3848...3374f4cce045

git log b5758d0d3848..3374f4cce045 --no-merges --oneline
3374f4cce Roll src/third_party/skia 8b35379ae1f1..32262da42bed (8 commits) (flutter/engine#6752)
61dbcdadf Roll src/third_party/skia e71e9ef311ba..8b35379ae1f1 (6 commits) (flutter/engine#6751)
c9b36fa11 Roll src/third_party/skia 51916083e752..e71e9ef311ba (1 commits) (flutter/engine#6750)
1a5a083de Roll src/third_party/skia 0a8b4e1acbd6..51916083e752 (2 commits) (flutter/engine#6749)
551d7f133 Roll src/third_party/skia 16d91aaf44fa..0a8b4e1acbd6 (1 commits) (flutter/engine#6748)
86feaccbf Roll src/third_party/skia 99485ace81ac..16d91aaf44fa (1 commits) (flutter/engine#6747)
4453e42ab Roll src/third_party/skia 2b21e88ed6dd..99485ace81ac (1 commits) (flutter/engine#6746)
fafef227a Roll src/third_party/skia 7e4081554d06..2b21e88ed6dd (1 commits) (flutter/engine#6745)
5d57e8af4 Roll src/third_party/skia b5ae3b5afc29..7e4081554d06 (1 commits) (flutter/engine#6744)
0e6b1e618 Roll src/third_party/skia e1b1d056fed9..b5ae3b5afc29 (3 commits) (flutter/engine#6743)
3429791c5 Roll src/third_party/skia f1ec3918534f..e1b1d056fed9 (1 commits) (flutter/engine#6742)
c5fa47a3c Roll src/third_party/skia 5d5de8bc79aa..f1ec3918534f (3 commits) (flutter/engine#6741)
be97304da Roll src/third_party/skia 1edff303fddb..5d5de8bc79aa (4 commits) (flutter/engine#6740)
731045e83 Roll freetype2 to a10b062df0c8958d69377aa04ea6554a9961a111 (flutter/engine#6738)
dd32b3fbc Roll src/third_party/skia 13245412d49e..1edff303fddb (6 commits) (flutter/engine#6739)
50ecdf965 Roll src/third_party/skia 3bfe9665aabc..13245412d49e (15 commits) (flutter/engine#6737)
96f7f344f Update scene_update_context to match recent PaintContext changes. (flutter/engine#6736)


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https://github.com/flutter/flutter/issues/22595

This rewrites the sample code analysis script to be a little less of a hack (but still not pretty), and to handle snippets as well.

It also changes the semantics of how sample code is handled: the namespace for the sample code is now limited to the file that it appears in, so some additional "Examples can assume:" blocks were added. The upside of this is that there will be far fewer name collisions.

I fixed the output too: no longer will you get 4000 lines of numbered output with the error at the top and have to grep for the actual problem. It gives the filename and line number of the original location of the code (in the comment in the tree), and prints out the source code on the line that caused the problem along with the error.

For snippets, it prints out the location of the start of the snippet and the source code line that causes the problem. It can't print out the original line, because snippets get formatted when they are written, so the line might not be in the same place.

This stops reading from pipe-to-file log after the build is completed. Attempting to read from pipe-to-file keeps open blocked because nobody is going to write into that pipe.

It's not usual for this not to be set, but it affected at least one user (#23909) and there are a non-zero number of people online saying it's not set. It's better that we don't crash.

Fixes #23909.

`RenderEditable.paint` assumes that if the length of the text fits within the
visible region, then the text will be rendered at the start of the region and be
completely visible. This is not always true, since the text may still be
rendered at an offset if an animation is ongoing when the text begins to fit.

This fixes #22288 and #14121