Features/detect available min api

[Bluebugs]

Description:

With latest NDK r25.b, I do not have the same minimum available API version for the compiler. To make it a bit more resilient to this kind of change, the code in the PR will automatically probe the filesystem to find the lowest available version.

This are all internal change and does not impact any ABI/API outside of fyne command line.

Checklist:

• Tests included.
• Lint and formatter run with no errors.
• Tests all pass.

Where applicable:

• Public APIs match existing style and have Since: line.
• Any breaking changes have a deprecation path or have been discussed.
• Updated the vendor folder (using go mod vendor).
• Check for binary size increases when importing new modules.

[coveralls]

Coverage decreased (-0.1%) to 61.413% when pulling 6b119e0 on Bluebugs:features/detect-available-minAPI into f4be32d on fyne-io:develop.

[andydotxyz]

Pretty sure this will resolve #3066

[toaster]

LGTM