Move tools tests into a general.shard directory in preparation to changing how we shard tools tests (#36108)

Fixes #24158
Re-lands #24173

This reverts commit 97e03104.

Landing on red to hopefully make less red on the board.

TBR=@goderbauer

Fixes #24158

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

When switching between channels, we were leaving around the version freshness stamp file (bin/cache/flutter_version_check.stamp), which meant that the flutter tool would read from that file to see what the cached date of the most recent commit to the current channel (branch) was. The problem was that since the file was created while on the previous channel, the cached date was for the wrong channel, so if you switch from master to beta, flutter would think that the channel was out of date, and a new version was available, at least for three days after the first time it checked (after three days since the last time the freshness was checked, the cached date would get updated).

This PR modifies the channel command to remove that stamp file whenever the user switches channels, so that the cached date will be from the right channel when it is recreated.

Fixes #21134

* Upgrade everything except matcher.
* Roll matcher (and test)
* Adjust tests that depend on flutter:test directly to depend on a shim
* Require use of package:test shim and remove other references to package:test

* Revert "Revert "Move mockito to 3.0.0-alpha. (#15949)" (#15979)"

This reverts commit e59651f9.

* More thenReturn to thenAnswer when mocking Futures

* Revert "More thenReturn to thenAnswer when mocking Futures"

This reverts commit 194d2cf41754ad171efd6bb5898cf73bce5a75ab as we are reverting engine roll.

* Revert "Revert "More thenReturn to thenAnswer when mocking Futures""

This reverts commit 52c9e96b304b220f66d78a252fccea0c8e0ef24c.

* Add dependency override

* Fix issue

This reverts commit a7e62258 as there are failing tests.

* Move mockito to 3.0.0-alpha.

This is needed so it matches mockito version used internally.

* Pick up +2 for the fixes

* Fix whenReturn in fuchsia_remote_debug_protocol

* more thenReturn becomes thenAnswer

* more thenReturn becomes thenAnswer

* more thenReturn becomes thenAnswer

* Use a set to remove duplicate channel names

* Add test for git command

`all.dart` is no longer needed. Furthermore, it causes tests to
be skipped, or to silently fail to run anything.

Fixes #7941

* Remove the workaround that pinned args to v0.13.6
This reverts most of the changes in commit 6331b6c8
* throw exception if exit code is not an integer
* rework command infrastructure to throw ToolExit when non-zero exitCode
* convert commands to return Future<Null>
* cleanup remaining commands to use throwToolExit for non-zero exit code
* remove isUnusual exception message
* add type annotations for updated args package

* adjust channel_test to be less specific
fixes https://github.com/flutter/flutter/issues/5716

* add flutter channel command
fixes https://github.com/flutter/flutter/issues/2513

* fix test

* address comments

* remove unused imports

* fix lints