This moves the docs generation and gallery upload to Cirrus CI, which is another step in turning off
Travis.

Fixes #19523

Two clients have run into this in the past so adding a bit of documentation to make it clear. See https://github.com/flutter/flutter/issues/19849 for one example.

72a38a6b1 Build Android engine in presubmit using Cirrus and GCE (#5882)
f9f40badd Log uncaught exceptions from JNI calls at a higher priority (#5891)
723b2784d Update license script README (#5890)
9420da1e2 Roll src/third_party/skia 9acfc6cac2c6..227424b57d28 (10 commits) (#5888)
27c9de59b Roll src/third_party/skia 55b1e6168454..9acfc6cac2c6 (1 commits) (#5887)
8b8c52ed7 Roll src/third_party/skia b935cf8e12d7..55b1e6168454 (1 commits) (#5886)
89602cc64 [scenic] Expose compositor context from rasterizer. (#5739)
9baeb9c1a Roll src/third_party/skia 5f1dc76d0cec..b935cf8e12d7 (1 commits) (#5885)

Fix the gradle templates so that they default to values rather than throw build exceptions. (#19916)

When creating a new project, the build fails with an error similar to:

"versionCode not found. Define flutter.versionCode in the local.properties file."

This puts developers in the untenable situation of having to edit a file with local paths, but being unable to check it in.

This changes the templates to default to using versionCode 1 and version "1.0" if they are not defined in the local.properties file.

Fixes #18983.

This reverts commit e52eeba3.

* Revert "Revert flutter/flutter#19592 (#19861)"

This reverts commit 00aac68e.

* Revert "roll engine to 6f7bdc9fabef810b14577deef5cf330029fd290e (#19848)"

This reverts commit 8b056296.

It was causing problems rolling Flutter into Fuchsia

This reverts commit 0636c6fe.

Disallow calling stop() or cancel() multiple times. This means that
when you use startProgress you have to more carefully think about what
exactly is going on.

Properly cancel startProgress in non-ANSI situations, so that
back-to-back startProgress calls all render to the console.

Pull in new versions of packages with fixes for SCREAMING CAPS CONSTANTS.

* Revert "Revert "Roll engine to 7d17da76d (#19785)" (#19792)"

This reverts commit e1a3e1bf.

This reverts commit 8adecb62.

```
7d17da76d Package Skia licenses into a separate file from other third party libraries (#5861)
d2d8bf394 Pass touch events to embedded Android views with dispatchTouchEvents.
216908652 Synthesize Android MotionEvents with the long form obtain method.
0b4432769 Roll src/third_party/skia 396661825f45..1c94a8fabed7 (8 commits) (#5859)
f50e218d9 Rename clip mode to clip behavior (#5853)
42bd86d6d Make the virtual display's presentation window non focusable. (#5845)
a726e1d85 Roll src/third_party/skia c062b6be5a01..396661825f45 (3 commits) (#5857)
3fa83d2d2 Roll src/third_party/skia 15020ea2cf44..c062b6be5a01 (1 commits) (#5856)
75ad43954 Roll src/third_party/skia 4c7a750e5543..15020ea2cf44 (1 commits) (#5855)
5cd8b4530 Roll src/third_party/skia 75e5406be66a..4c7a750e5543 (2 commits) (#5854)
e12b52841 Roll src/third_party/skia b8eeb808d84f..75e5406be66a (17 commits) (#5852)
5bc1e68b6 Remove check_roll from Travis (#5846)
```

Our Cirrus Windows tests were not really working: they reported success even when failing.

This should fix several problems with the Cirrus Windows tests.