Exception in Flutter Gallery / Dialogs Demo #6826

* convert flutter commands to use ToolExit for non-zero exit code
* add convenience method throwToolExit
* print ToolExit message iff not null

The added printTrace statements are causing problems when running tests locally on Linux.
This reverts commit 546cef52.

These define a TextTheme and IconTheme that contrast with the accent
colour brightness. Also adjust default accentColorBrightness to match
Material spec examples (dark text/icons on teal in Dark theme).

Update material components to use accentTextTheme, accentIconTheme:
* DatePicker selection
* Floating action button icon
* TimePicker selection
* Slider label text

- [x] Return the reload message even when paused at a breakpoint.
- [x] Only initialize context members if they aren't already initialized.

Fixes https://github.com/flutter/flutter/issues/6690

Also add a version of the Gallery smoke test that enables semantics

- [x] Stop tracking time to first frame because it is unreliable.
- [x] Track time to complete reassemble instead.

I was in here trying to figure out why we rebuild sky_services (the
answer is, because we rebuild every package we've ever downloaded, but
that's not really a problem for new users so whatever), and while I
was here I did some cleanup.

- [x] Remove old benchmark code from the non-hot runner.
- [x] Remove some dead code.
- [x] Fix a throw that should be a rethrow.

...by reverting us to an earlier dartdoc package.

Also I added a sanity test to make sure that we don't regress this again.

* Commit the IhtelliJ project metadata for the Gallery

* Add default run config for Gallery

* Add back ignore of .idea per review feedback

The IntelliJ plugin will use this as a baseline to ensure that the installed tools support the expected message formats.

To see where this applies, look at https://github.com/flutter/flutter-intellij/pull/426

The changes we’re checking for were introduced in https://github.com/flutter/flutter/commit/1f1adcaa0e563cb68ec5f0d2f82efc9759be1221

Fixes https://github.com/flutter/flutter/issues/6603