Sometimes you have several listenables, but you want to hand them to an
API (e.g. CustomPainter) that only expects one.

* Animate size of label text over text fields.

Also fade in the hintText so it doesn't pop in immediately as the label
text slides up.

Fixes https://github.com/flutter/flutter/issues/7217

* rm annotations

* test

* rename

Without this, an FLX with no assets may be completely empty in AOT mode.
This will result in a warning when the engine's unzip library tries to
parse the FLX.

Fixes https://github.com/flutter/flutter/issues/7060

See https://github.com/flutter/flutter/issues/7248

Fixes https://github.com/flutter/flutter/issues/7017

Fixes https://github.com/flutter/flutter/issues/6943

Fix _DragAvatar to display in the proper position for Overlays whose Point.origin is not the global Point.origin. (#7223)

The default rpc.Peer constructor was applying a transformer that filters
out these errors.

See https://github.com/flutter/flutter/issues/7174

This tests against the failure that was fixed in #7189

This fixes an infinite loop in the code that walks the parent
context chain looking for a variable.

This also includes a fix in build_info.dart whereby if the context
is set but the config is not yet set, we were trying to dereference
null.

* have flutter run --machine log to stdout

* add a test

* add docs; fix type annotation lint

* s/sky/flutter/ in Android templates

* update engine.version with a compatible engine version

* replace more SkyActivity references with FlutterActivity

This argument will enable mocking of os-layer process invocations,
where the mock behavior will come from replaying a previously-
recorded set of invocations. At the point of process invocation,
the key metadata for the invocation will be looked up in the
recording's manifest, and iff a matching record exists in the
manifest, the process will be mocked out with data derived from
the corresponding recorded process (e.g. stdout, stderr, exit code).