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).

This moves the various copies of port forwarding code in the Device subclasses into the ProtocolDiscovery class.

* move port forwarding to a common location
* throw exception if protocol Uri is not discovered or port forwarding fails
* cancel discovery protocol subscriptions on iOS launches (wasn't happening before)
* fix iOS port forwarding to match other implementations
* add tests

It is not enabled by default in the VM because applications not launched via the tools may try to connect with the debugger. This causes the debugger and the IDE to hang on Mac.

Fixes https://github.com/flutter/flutter/issues/7035

Includes fixes to the VM and analyzer.  Hopefully final RC.

* Use touch to avoid race condition in file modification test

* Remove unused import