Migrate to SAF for file access

[syntaxerror247]

This PR migrates storage access to SAF and removes the MANAGE_EXTERNAL_STORAGE permission.

The implementation is still in progress (code is still a mess and I need to move utils methods to seperate file etc.). I just created this PR so you guys can properly test the workflow. Feedback is welcome.
You can test it using the GHA artifacts for this PR.

For testing release builds, either:

• Use the editor from this PR: Android Editor: Copy keystore to temp file during export godot#116161
• Or manually place your release keystore in [project root]/android/build/.android and rename to release.keystore.

Debug builds work without any additional steps.

[syntaxerror247]

Converting this back to draft. I need to add a dialog that explains to users why the notification permission is required, and add support for custom gradle_build_directory.

[syntaxerror247]

Converting this back to draft. I need to add a dialog that explains to users why the notification permission is required, and add support for custom gradle_build_directory.

Done!

Restored support for a custom gradle_build_directory. The project card now also displays the Gradle build directory, to make it clear which entry belongs to which gradle project.

Added a dialog explaining why notification permission is required.

[syntaxerror247]

@m4gr3d Thanks for reviews, I've resolved all your comments.

[m4gr3d]

Looks good, great job!