Paying off technical debt...

Follow-up comments to #15984

This updates AppContext per the recommendations in #15352

Fixes #15352

* Revert "Revert "Add android license verification to doctor and some refactoring" (#14727)"

This reverts commit d2602947.

* Add tests, fix sdkManagerEnv and use it consistently, and rearrange Status object model

* AnsiSpinner needs to leave the cursor where it found it.

* fix tests

* Const constructor warning only shows up on windows...?

* Avoid crash if we can't find the home directory

* Make pathVarSeparator return a string in the mock

* Implement review comments

* Fix out-of-order problem on stop

* Fix packages tests when run off bots

* Tweak dependencies to make bots happy

* Review comment

Reports from that commit included:

* Doctor hanging
* Doctor prompting to install JDK
* AnsiStatus.cancel() printing elapsed time and extra newline
* Printing extra spinner character at the end of each line

* Initial version, seems to work

* Unit test for android license checker

* Cleanups

* Windows analyzer wants const.

* Refinements to timeout

* review comments

* Forgot a nit

* Flatten change out from lots of merges and temporary hacks for #7224

* Expand fakes to cover cases where doctor passes

* -v != --verbose

* Cosmetic touchups

* delint

* Clean up summary line, add a switch for review comments

* Review comments

* nit

* review comment

* review comments

* Populate AnsiTerminal in context for daemon launches

* Strip out AnsiTerminal additions to context since they are no longer needed

* Get rid of static version methods which ignore the AppContext

* Review comments

* Review Comments

* Make branch behave the same as original implementation

* Fix tests

* executable.dart#main() depends on runner.dart#run()
* Refactor code such that non-commands don't depend on commands.

No code was actually changed in this PR - code was merely moved from
point A to point B.

* Make clean command top level

Fixes https://github.com/flutter/flutter/issues/10783

* remove backwards

* add a --machine mode to flutter config

* review feedback

Currently this just prints the observatory URL as a JSON event.
Refactored the code to make this fit in.

* first pass

* improvements

* extract terminal.dart

* rebase

* add default terminal to context

* The analyzer wants the ../ imports in front of the ./ imports

* review notes

This message will be picked up by IntelliJ and shown to the user in a toast.

This should make the message in Travis logs look better.

It's no longer needed with the latest Dart SDK roll.

- [x] Don't use package:stack_trace.
- [x] Don't use Chain.capture.
- [x] Fix an instance of aggressive catching of exceptions

Related #8742

* Make ProcessSignals portable

This removes the need to wrap unsupported signals with in `if (!platform.isWindows) ..`.

It also allows us to implement a work around for breaking the Windows console when flutter is exited with Ctrl+C.

* review comments

* adding tests

* add license header

It was resulting in weird situations where the tool would dump an
error message and stack but not quit, or would fail hard but then just
hang.

Instead, specifically catch errors you expect. As an example of this,
there's one error we expect from the DartDependencySetBuilder, so we
catch that one, turn it into a dedicated exception class, then in the
caller catch that specific exception.

* prefer const constructors

* fix double throw

This adds the test harness for record/replay tests.

* add crash reporting without enabling it

* do not drop futures on the floor

* return exitCode from executable run

* debug travis

* remove unnecessary todo

* rename local fs getter

This adds support for a `--bug-report` flag, which is a recording
that:
  - includes the arguments that were passed to the command runner
  - is zipped up for easy attachment in Guthub issues

* Teach flutter tools to find gradle

Flutter tools will now use Gradle from Android Studio, which is now found automatically.

flutter doctor will verify that Android Studio has been installed, and that the included Gradle is at least version 2.14.1.

It is still possible to manually configure the path to Android Studio (flutter config --android-studio-dir=XXX) or Gradle (flutter config --gradle-dir=XXX), but this should only be necessary if they're installed somewhere non-standard.

Only tested on Linux and macOS for now.

Fixes #8131

Artifacts are now located in a central place.
This will enable us to downlaod artifacts when we need them (instead of
downloading them all upfront).
This also makes replacing sky_snapshot with gen_snapshot easier.

Replaces unprintable characters with alternative symbols.