[flutter_tool] Refactor Logger and Terminal to (mostly) no longer depend directly on context (#47269)

* Update project.pbxproj files to say Flutter rather than Chromium

Also, the templates now have an empty organization so that we don't cause people to give their apps a Flutter copyright.

* Update the copyright notice checker to require a standard notice on all files

* Update copyrights on Dart files. (This was a mechanical commit.)

* Fix weird license headers on Dart files that deviate from our conventions; relicense Shrine.

Some were already marked "The Flutter Authors", not clear why. Their
dates have been normalized. Some were missing the blank line after the
license. Some were randomly different in trivial ways for no apparent
reason (e.g. missing the trailing period).

* Clean up the copyrights in non-Dart files. (Manual edits.)

Also, make sure templates don't have copyrights.

* Fix some more ORGANIZATIONNAMEs

Allow ProjectFileInvalidator to be overridden with a different
implementation.

I stole this from https://github.com/flutter/flutter/pull/39217.

Empirical measurements indicate on the network file system we use
internally, using `FileStat.stat` on thousands of files is much
faster than using `FileStat.statSync`. (It can be slower for files
on a local SSD, however.)

Add a flag to `ProjectFileInvalidator.findInvalidated` to let it
use `FileStat.stat` instead of `FileStat.statSync` when scanning for
modified files.  This can be enabled by overriding `HotRunnerConfig`.

I considered creating a separate, asynchronous version of
`findInvalidated`, but that led to more code duplication than I
liked, and it would be harder to avoid drift between the versions.

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.

In preparation for some refactoring that I will be doing to
`ProjectFileInvalidator.findInvalidated`, make its code a bit
clearer:
* Indicate which arguments may be null.
* Don't bother calling `FileStat.statSync` on the `.packages` file
  for the initial load.  This makes the checks for the `.packages`
  file consistent with those for other files.
* Use `DateTime.isAfter()` instead of comparing microseconds
  ourselves.

While I was touching this file, I also removed some unnecessary
comparisons to `false`. (`_ManifestAssetBundle.wasBuiltOnce()` is the
only implementation I can find of `AssetBundle.wasBuiltOnce()`, and
it never returns `null`.)

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

* Use source list from the compiler to track invalidated files.

* Revert accidental change

* Fix first-time-seen-the-file logic

* Fix/simplify invalidate logic now that we can rely on compiler to let us know what is the cut-off point for invalidation.

* Update devfs mock to accommodate for new fields

* Fix deleted files case

* Analyzer found missing final

* 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