This updates AppContext per the recommendations in #15352

Fixes #15352

It was failing in the case of an AppContext being in scope
but not having a `BotDetector` seeded in it.

* Fix packages tests when run off bots

* Tweak dependencies to make bots happy

* Review comment

* First version

* Prevent modification of .flutter during analytics test

* Pass in directory and override analyzer warning due to conditional import

* Review comments

I got tired of drive-by spelling fixes, so I figured I'd just take care of them all at once.

This only corrects errors in the dartdocs, not regular comments, and I skipped any sample code in the dartdocs. It doesn't touch any identifiers in the dartdocs either. No code changes, just comments.

* enable lint prefer_foreach

* fix tests

* round 2

* deal with null futures

* review

* review

* review

* review

* perform the initial poll for devices quicker

* add a Poller class

* test the new Poller class

Eagerly generate local.properties, and always update the flutter.sdk
setting in it, in case FLUTTER_ROOT has changed.

Fixes #8365.
Fixes #9716 - at least the specific issue reported. My Android Studio
still complains about Gradle versions - it ships with v3.2, but requires
v3.3...

Add a 'generate dependencies' task to the Gradle build, which checks if
the snapshot dependencies file exists, and runs an extra build before
the actual FlutterTask if it doesn't. This makes the first build slower,
but sub-sequent builds (without source changes) much faster.

Fixes #9717.

* Populate PUB_ENVIRONMENT for initial pub get

* review comments

* change order

FlutterCommand.runCommand subclasses can optionally return a FlutterCommandResult which is used to append additional analytics. 

Fix flutter run timing report and add a bunch of dimensional data

* improve the logger ui a bit for elapsed times

* invert param

* update daemon.dart

This ensures that accidental usages of dart:io's
file API don't creep in over time.

This removes direct file access from within flutter_tools
in favor of using `package:file` via a `FileSystem` that's
accessed via the `ApplicationContext`.

This lays the groundwork for us to be able to easily swap
out the underlying file system when running Flutter tools,
which will be used to provide a record/replay file system,
analogous to what we have for process invocations.

* make app ids more unique

* in-line the uuid class

* making flutter run work with gradle

* locate android studio

* add test for settings

* review comments

* refactor the --resident run option into a separate file

* update daemon to run --resident apps

* re-plumbing daemon start

* send app logs

* update tests

* review changes

* fix test runner

* remove PackageMap.createGlobalInstance; rely on the ctor

* review comments

* show build progress; print app sizes

* add todo

* review comments

* remove unused import

* dissallow -release mode on emulators

* have the help text print the default mode

* rename service_protocol.dart to protocol_discovery.dart

* add a wrapper around the obs. protocol

* use json-rpc in run

* consolidate obs. code; implement flutter run --benchmark

* review comments

* avoid sending analytics on ci systems

* review comments

* use the new cache code to locate more artifacts

* add todo

* review comments