Fixes:
- #132258

Refactor the globals getter for `Analytics` to be in the context instead of having a default fallback. The current state of the tool creates a new instance every time `globals.analytics` was called

Addresses issue:
- https://github.com/flutter/flutter/issues/128535

Give channel descriptions in `flutter channel`, use branch instead of upstream for channel name (#126936)

## How we determine the channel name

Historically, we used the current branch's upstream to figure out the current channel name. I have no idea why. I traced it back to https://github.com/flutter/flutter/pull/446/files where @abarth implement this and I reviewed that PR and left no comment on it at the time.

I think this is confusing. You can be on a branch and it tells you that your channel is different. That seems weird.

This PR changes the logic to uses the current branch as the channel name.

## How we display channels

The main reason this PR exists is to add channel descriptions to the `flutter channel` list:

```
ianh@burmese:~/dev/flutter/packages/flutter_tools$ flutter channel
Flutter channels:
  master (tip of tree, for contributors)
  main (tip of tree, follows master channel)
  beta (updated monthly, recommended for experienced users)
  stable (updated quarterly, for new users and for production app releases)
* foo_bar

Currently not on an official channel.
ianh@burmese:~/dev/flutter/packages/flutter_tools$
```

## Other changes

I made a few other changes while I was at it:

* If you're not on an official channel, we used to imply `--show-all`, but now we don't, we just show the official channels plus yours. This avoids flooding the screen in the case the user is on a weird channel and just wants to know what channel they're on.
* I made the tool more consistent about how it handles unofficial branches. Now it's always `[user branch]`.
* I slightly adjusted how unknown versions are rendered so it's clearer the version is unknown rather than just having the word "Unknown" floating in the output without context.
* Simplified some of the code.
* Made some of the tests more strict (checking all output rather than just some aspects of it).
* Changed the MockFlutterVersion to implement the FlutterVersion API more strictly.
* I made sure we escape the output to `.metadata` to avoid potential injection bugs (previously we just inlined the version and channel name verbatim with no escaping, which is super sketchy).
* Tweaked the help text for the `downgrade` command to be clearer.
* Removed some misleading text in some error messages.
* Made the `.metadata` generator consistent with the template file.
* Removed some obsolete code to do with the `dev` branch.

## Reviewer notes

I'm worried that there are implications to some of these changes that I am not aware of, so please don't assume I know what I'm doing when reviewing this code. :-)

Relands #126086, which was reverted by #126569.

Reverts flutter/flutter#126086.

This PR changed the interfaces of some classes, namely `AndroidSdk`, and deleted a global.

These classes had custom overrides in g3 that were not updated with a g3fix, so this PR has broken tests. See https://b.corp.google.com/issues/281945232 (non-public link)

This is the first step in unifying Java-finding logic across the tool. If curious, see #126029 for an example of what all the changes will probably entail.

Moves java-related functionality like `AndroidSdk.findJavaHome` to a new class, `Java`.

See tracking issue https://github.com/flutter/flutter/issues/126126 for more.

The first of many PRs for transitioning to `package:unified_analytics`.
This PR is only focused on disabling and enabling telemetry via the
`flutter config --[no-]analytics` flag

Fixes: https://github.com/flutter/flutter/issues/121617

## Pre-launch Checklist

- [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 `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel
on [Discord].

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[test-exempt]:
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---------
Co-authored-by: Christopher Fujino <fujino@google.com>
Co-authored-by: Christopher Fujino <christopherfujino@gmail.com>

Re-land of https://github.com/flutter/flutter/pull/123297 without any of
the commits at the end attempting to fix customer-testing.

Fixes https://github.com/flutter/flutter/issues/118810

Revert "[flutter_tools] Remove --no-sound-null-safety #3"

[flutter_tools] Remove --no-sound-null-safety #3

This reverts commit 275ab9c6.

Revert "Reland "Remove references to Observatory (#118577)""

This reverts commit 298d8c76.

This reverts commit 2df140f4.

Observatory is being deprecated for Dart 3.0 so it should no longer be
referenced in tooling messaging / flags.

See https://github.com/dart-lang/sdk/issues/50233

* Update flutter_tools to look for new VM service message

The Dart SDK will soon move away from the current Observatory message:

"Observatory listening on ..."

To a new message that no longer references Observatory:

"Dart VM Service listening on ..."

This change updates all tests with mocks to check for the new message
and also adds support for the new message in ProtocolDiscovery.

See https://github.com/dart-lang/sdk/issues/46756

* Fix some parsing locations

* Fix analysis failures

* Update message

* Remove extra comment

* Update message

* Add globals prefix

This reverts commit 00658736.