New feature in upcoming Dart 3.2. See https://github.com/dart-lang/language/issues/2020. Feature is enabled by bumping the min SDK version to 3.2.

Part of https://github.com/flutter/flutter/issues/134476.

Context: https://github.com/flutter/flutter/issues/131862

This PR injects a "realm" component to the storage base URL when the contents of the file `bin/internal/engine.realm` is non-empty.

As documented in the PR, when the realm is `flutter_archives_v2`, and `bin/internal/engine.version` contains the commit hash for a commit in a `flutter/engine` PR, then the artifacts pulled by the tool will be the artifacts built by the presubmit checks for the PR.

This works for everything but the following two cases:
1. Fuchsia artifacts are not uploaded to CIPD by the Fuchsia presubmit builds.
2. Web artifacts are not uploaded to gstatic by the web engine presubmit builds.

For (1), the flutter/flutter presubmit `fuchsia_precache` is driven by a shell script outside of the repo. It will fail when the `engine.version` and `engine.realm` don't point to a post-submit engine commit.

For (2), the flutter/flutter web presubmit tests that refer to artifacts in gstatic hang when the artifacts aren't found, so this PR skips them.

Presubmit testing and CI testing of Flutter using a custom storage location for engine artifacts must be able to use the --fatal-warnings flag without failing due to the custom artifact location.

This change adds an option that makes this warning non-fatal. The new --no-fatal-storage-url-warning flag makes the --fatal-warnings flag ignore the warning that a custom artifact download URL is being used by setting the environment variable FLUTTER_STORAGE_BASE_URL.

Bug: #127683

- [X ] I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
- [X ] I read the [Tree Hygiene] wiki page, which explains my responsibilities.
- [X ] I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement].
- [X ] I signed the [CLA].
- [X ] I listed at least one issue that this PR fixes in the description above.
- [X ] I updated/added relevant documentation (doc comments with `///`).

The newly updated lint will soon flag for-each in collections.

See discussion: https://github.com/dart-lang/linter/pull/4383

/cc @goderbauer

Fixes https://github.com/flutter/flutter/issues/126705

Migrate activation issue template to Github form issues

...and various other minor cleanup:

* Moved "FLUTTER_STORAGE_BASE_URL" into a constant throughout the code. There are other strings that we should do that to but this one was relevant to the code I was changing.

* Fixed the logger's handling of slow warnings. Previously it deleted too much text. Fixed the test for that to actually verify it entirely, too.

* Made the logger delete the slow warning when it's finished.

* Fixed 'Please choose one (To quit, press "q/Q")' message to be the cleaner 'Please choose one (or "q" to quit)'.

* Added a debug toString to ValidationResult for debugging purposes (not used).

* In http_host_validator:

  - Shortened constant names to be clearer (e.g. kPubDevHttpHost -> kPubDev).
  - Added GitHub as a tested host since when you run `flutter` we hit that immediately.
  - Renamed the check "Network resources".
  - Updated the `slowWarning` of the check to say which hosts are pending.
  - Removed all timeout logic. Timeouts violate our style guide.
  - Removed `int.parse(... ?? '10')`; passing a constant to `int.parse` is inefficient.
  - Replaced the `_HostValidationResult` class with `String?` for simplicity.
  - Improved the error messages to be more detailed.
  - Removed all checks that dependened on the stringification of exceptions. That's very brittle.
  - Added a warning specifically for HandshakeException that talks about the implications (MITM attacks).
  - Replaced exception-message-parsing logic with just calling `Uri.tryParse` and validating the result.
  - Replaced a lot of list-filtering logic with just a single for loop to check the results.
  - Replaced code that added a constant to a known-empty list with just returning a constant list.
  - Revamped the logic for deciding which hosts to check to just use a single chain of if/else blocks instead of getters, lists literals with `if` expressions, `??`, functions, etc spread over multiple places in the code.

*  Only log warning for storage base url

*  Add test

*  Add the link to the test

*  Remove the test

*  Remove the extra import

* dart fix --apply

* manual fixes

* fix after merge conflicts

* review

Co-authored-by: Christopher Fujino <christopherfujino@gmail.com>

* Add DevTools version to `flutter --version` output.

* review comments

* fix test

* add explanatory comment

* dummy commit to kick bots
Co-authored-by: Christopher Fujino <christopherfujino@gmail.com>

This reverts commit 00658736.

This reverts commit cb378edc.

This changes the "Waiting for another flutter command to release the startup lock..." message output so that it appears on stderr instead of stdout. When it appears on stdout, it can mess up collection of the output. For instance, if you run flutter --version --machine and you're expecting JSON output, then you'll get non-JSON output even though the lock is released and you eventually would get what you're asking for.