Enable plugin_test_linux

* Fix binary path

* Enable in presubmit

* Add Linux unit tests to plugin template

Adds an example native unit test to the plugin template for Linux,
matching the structure we use for our 1P plugin unit tests. Once these
have been added for all platforms+languages, they will be documented on
a new plugin development page to explain their use.

While ideally we would adjust the engine APIs first to allow for testing
the method call handler directly, it's unclear when we will have time
for that work, and for a complex plugin most of the testing wouldn't be
at that layer anyway, so having the structure in place with the
limitations documented is still a significant improvement over having
nothing in the template.

Part of https://github.com/flutter/flutter/issues/82458

* Add creation test

* Add integration tests

* Missing newlines

* test owner

* Typo

* Add Java tests

* Add Kotlin

* Add integration testing

* Add cerate tests

* Add Windows unit tests to plugin template

Adds an example native unit test to the plugin template for Windows,
matching the format we use for our 1P plugin example app unit tests.
Once these have been added for all platforms+languages, they will be
documented on a new plugin development page to explain their use.

Since we don't appear to be running our current plugin e2e tests for
Windows, this adds a new configuration to run them. I haven't
`led`-tested this, so it may not work, but this will give a starting
point for getting them running.

Part of https://github.com/flutter/flutter/issues/82458

* Minor fix

* Add test owner

* Fix typo

* Fix test feature flag

* Improve Swift plugin implementation

* Add iOS tests

* Review feedback on structure

* Remove duplicate scheme file

* Add macOS

* Add iOS

* swift test tweaks

* unit tests

* Whitespace

* Add e2e tests

(Attempt to reland #85993)

This reverts commit 2175e64e.

Migrate core devicelab framework to null safety.

* 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

* Fix plugin template

* Add test of plugin template working

* 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

Fixes the build after my module rename broke the Windows tests.

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

All temporary directory start with `flutter_` and have their random component separated from the name by a period, as in `flutter_test_bundle.YFYQMY`.

I've tried to find some of the places where we didn't cleanly delete temporary directories, too. This greatly reduces, though it does not entirely eliminate, the directories we leave behind when running tests, especially `flutter_tools` tests.

While I was at it I standardized on `tempDir` as the variable name for temporary directories, since it was the most common, removing occurrences of `temp` and `tmp`, among others.

Also I factored out some common code that used to catch exceptions that happen on Windows, and made more places use that pattern.