[CP-stable]Fix Android license detection for cmdline-tools 23.0+ - #192133

## Description

Fixes flutter#191487

Android SDK cmdline-tools 23.0 deprecated `sdkmanager --licenses` in
favor of the new `android` CLI. Running `sdkmanager --licenses` now only
prints a deprecation warning instead of the parseable license summary
Flutter previously relied on:

```
WARNING: The SDK Manager CLI tool (sdkmanager) is deprecated. Android CLI will be used instead.
The 'android' binary can also be found in the cmdline-tools directory, and 'android sdk' is the replacement for 'sdkmanager'.
To learn more about the Android CLI and how to use it, see the documentation (https://d.android.com/tools/agents/android-cli)
Warning: The --licenses option is no longer needed.
```

None of the existing regexes in `licensesAccepted` match this output, so
`flutter doctor` incorrectly reports `Android license status unknown`
even when licenses are actually accepted.

## Approach

I initially considered treating the new deprecation message as
`LicensesAccepted.all`, but testing against a real cmdline-tools 23.0
install showed this message prints identically whether or not the
licenses directory exists — so it can't be trusted as a signal of actual
license state. I verified this by temporarily renaming my
`<sdk>/licenses` directory and re-running `sdkmanager --licenses`; the
output was byte-for-byte identical either way.

I also checked the new `android` CLI's `--help` output (`sdk`, `sdk
install`, `info`) — there's no license-status subcommand or flag exposed
in this version, so there's no better structured signal to query
instead.

Since the SDK's actual license acceptance state is still tracked on disk
under `<sdk>/licenses/` (this is presumably what Gradle checks directly,
since Gradle builds still succeed after this cmdline-tools update), this
PR adds a narrow, additive fallback:

- When `sdkmanager`'s output matches the specific new-CLI deprecation
message (and only then — not for arbitrary unparseable/garbage output),
`licensesAccepted` checks the `licenses/` directory on disk directly
instead of trusting stdout.
- All existing regex-based parsing for older `sdkmanager` versions is
untouched.

## Known limitation

This fallback can only distinguish "some license files are present and
non-empty" (→ `all`) from "no license files at all" (→ `none`). It
cannot reproduce the previous `LicensesAccepted.some` state for the new
CLI, since that information is no longer exposed by the tool in any form
I could find. Happy to adjust the approach if maintainers have a
preference here.

## Tests

Added two regression tests reproducing the exact real-world output
captured from a Windows machine running cmdline-tools 23.0:
- `licensesAccepted falls back to the licenses directory when sdkmanager
output is unparseable (new Android CLI, licenses present)`
- `licensesAccepted falls back to none when sdkmanager output is
unparseable and no licenses are present (new Android CLI, licenses
missing)`

All existing tests in `android_workflow_test.dart` continue to pass
(35/35).

Also manually verified end-to-end: `flutter doctor -v` on the affected
machine now correctly reports `All Android licenses accepted.` instead
of `Android license status unknown.`

---------

Co-authored-by: Gray Mackall <[email protected]>