This consolidates all of the non-template .gitignore rules into the top level .gitignore, to ignore common things more broadly, with less maintenance needed for the .gitignore files. Does not touch the templates, so that they still produce needed .gitignores as part of flutter create.

* delay taking screenshot to allow GPU thread to render the frame

* address comments

* Revert "Revert "fix --force-upgrade script; upgrade to the latest package versions (#12700)" (#12729)"

This reverts commit 7f0d4f4c.

* keep linter pinned at 0.1.35

This reverts commit 5b357500.

* fix updrade script; upgrade to the latest package versions

* exclude special dependencies from transitive closure

* fix stack trace handling in flutter_test due to stack_trace change

* change type on _emptyStackTrace

* Force upgrade update packages with improved update process.

* Update packages

* Revert "Update packages"

This reverts commit a37de26d3f4f7f5a15746ff791002625faa3d3c0.

* Add framework-side support for system text scale factor.

* Rolling engine to e3404b81a53ba3180c7623a6f2190ebb28518f30
  Additional changes rolled in with engine change:
    libtxt: implementation of GetRectsForRange that processes a line at a time - e3404b8
    Provide an entropy source to the Dart engine (#4161) - e1aa867
    libtxt: search for fallback fonts that can match emoji and CJK characters - 8061df1
    Roll skia to e4679fa06a. (#4157) - 267e7a8
    Update buildroot to 53fea9aebbcc39c6522731471a1a45960ee0685e (#4160) - 02ea7ae
    Revert engine Dart roll. (#4158) - 14aab33
    Add support for system text scale factor. (#4124) - b2a7f4b
    Include _http into sky_engine libraries for analyzer (#4154) - b930f10
    libtxt: Remove postprocess_line and improve tracking of X offsets - 86f95f0
    libtxt: remove redundant line_widths (#4152) - 14bf515
    Roll dart to ade37f931e90b0fdb8fe16d6bf6f089545da55b6 (#4151) - 6f1264f

Alignment will eventually replace FractionalOffset.

* Pin all dependencies ONCE AND FOR ALL

This replaces the secret `flutter update-packages --upgrade` with a destructive `flutter update-packages --force-upgrade` that actually goes and pins every dependency and transitive dependency in every flutter package to the same version.

* Add comments.

* only tap on widgets reachable by hit testing

* use FractionalOffset

* added tests

* check finder finds correct widget

* undo unintentional changes

* address comments

* style fix

* add Directionality in test

* fix analysis warning

* enable lint prefer_final_fields

* enable lint recursive_getters

* enable lint unnecessary_overrides

* upgrade to linter-0.1.35

* re-enable lint prefer_const_constructors

* address review comments

The flakiness of commands_test is generally visible via:

```
drive:stdout:   Expected: 'log: paint'
drive:stdout:     Actual: ''
drive:stdout:      Which: is different. Both strings start the same, but the actual value is missing the following trailing characters: log: paint ...
```

By returning the name of the test we will be able to understand if
another test is running by reading the `Actual` value

This reverts commit 8d07d3f6.

This reverts commit 5d9db106.

* Revert "Make plugins add their repos to projects in the consuming app (#11447)"

This reverts commit abe1e252.

* Revert "Support for custom build types on Android (#11354)"

This reverts commit 87eec719.

* Revert "add a profile() method (#11443)"

This reverts commit 561d17a8.

* Revert "Fix documentation based on dartdoc's warnings (#11428)"

This reverts commit 6655074b.

* Revert "Improve some docs around WillPopScope. (#11429)"

This reverts commit 58a28a29.

* Revert "temporarily disable broken driver test in integration_ui (#11440)"

This reverts commit 764515ec.

* Revert "style fix"

This reverts commit 00bfc866.

* Revert "tests for waitFor/waitForAbsent"

This reverts commit 31d2ee9c.

* Revert "Always evaluate the finder in `driver.waitFor()` and `driver.waitForAbsent()`"

This reverts commit 11d7c79b.

The main purpose of this PR is to make it so that when you set the
initial route and it's a hierarchical route (e.g. `/a/b/c`), it
implies multiple pushes, one for each step of the route (so in that
case, `/`, `/a`, `/a/b`, and `/a/b/c`, in that order). If any of those
routes don't exist, it falls back to '/'.

As part of doing that, I:

 * Changed the default for MaterialApp.initialRoute to honor the
   actual initial route.

 * Added a MaterialApp.onUnknownRoute for handling bad routes.

 * Added a feature to flutter_driver that allows the host test script
   and the device test app to communicate.

 * Added a test to make sure `flutter drive --route` works.
   (Hopefully that will also prove `flutter run --route` works, though
   this isn't testing the `flutter` tool's side of that. My main
   concern is over whether the engine side works.)

 * Fixed `flutter drive` to output the right target file name.

 * Changed how the stocks app represents its data, so that we can
   show a page for a stock before we know if it exists.

 * Made it possible to show a stock page that doesn't exist. It shows
   a progress indicator if we're loading the data, or else shows a
   message saying it doesn't exist.

 * Changed the pathing structure of routes in stocks to work more
   sanely.

 * Made search in the stocks app actually work (before it only worked
   if we happened to accidentally trigger a rebuild). Added a test.

 * Replaced some custom code in the stocks app with a BackButton.

 * Added a "color" feature to BackButton to support the stocks use case.

 * Spaced out the ErrorWidget text a bit more.

 * Added `RouteSettings.copyWith`, which I ended up not using.

 * Improved the error messages around routing.

While I was in some files I made a few formatting fixes, fixed some
code health issues, and also removed `flaky: true` from some devicelab
tests that have been stable for a while. Also added some documentation
here and there.

Under android/ directory, ignore:
GeneratedPluginRegistrant.java

Under ios/ directory, ignore:
GeneratedPluginRegistrant.h
GeneratedPluginRegistrant.m
Pods/

Ensure that showing the keyboard applies padding, reducing the view
height.