[flutter_tools] Fix avdmanager path detection

[GurjinderPartola]

The old Android SDK tools ($ANDROID_SDK_ROOT/tools/bin) have been deprecated in favor of the new cmdline-tools (see https://developer.android.com/studio/releases/sdk-tools).
The sdkmanager binary can be detected at both locations, this PR does the same for the avdmanager binary.

Fixes #64035.

Pre-launch Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I read the [Tree Hygiene] wiki page, which explains my responsibilities.
• I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement].
• I signed the [CLA].
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test-exempt.
• All existing and new tests are passing.

[jonahwilliams]

LGTM, thank you!