This reverts commit 3597bae6.

...because otherwise, processes that think they're manipulating your
filesystem will be doing crazy things the test is ignoring, leading to
(at best) failures and (at worst) flakes or disk corruption.

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

* some space formattings

* always use blocks in if-else if a block is used

* format spaces in for and while

* allow multiline if conditions

* fix missing space

* add trailing commas on list/map/parameters

* add trailing commas on Invocation with nb of arg>1

* add commas for widget containing widgets

* add trailing commas if instantiation contains trailing comma

* revert bad change

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

* 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

Note: In a cross-platform context `Uri.path` is not a valid file path. Allways use `fs.path.fromUri` to convert.

* Do not lower-case paths during canonicalization.

This breaks hot reload on some platfroms with case insensitive file systems.

* Add unit tests

If ensureDirectoryExists fails -- e.g. because a file file of the same
name as the directory to be created exists, ensure that we exit cleanly
with a useful error message.

* Add a check in case the flutter directory in .packages no longer exists. Clean up and prompt user

* Update documentation to use flutter packages get for end-users instead of flutter update-packages.

* Merge missing sdk error with the multiple sdk error. They're really the same thing.

* Use flutterPath in both checks.

* Change file_system’s copy folder to copy director which takes into account the file system

* Test support files

* Add test and split into 2 messages again.

* Move tests to run in memory file system's copy. Tested with dev/bots/test.sh

* Change file_system’s copy folder to copy director which takes into account the file system

* Address review comments.
Test with 2 different instances of file systems.