Migrates existing instantions of `--template plugin_ffi` to deal with Android 15 16kb memory pages.
Issue:
* https://github.com/flutter/flutter/issues/155933
@reidbaker I could only find migrations that run from the root application. However the file needing to be migrated is a plugin. The plugin is being referenced from the example in the example dir and that's where the migrator is run, so I wrote the code so that it walks up to find the plugin. Do you know of a way to run migrators to non-root projects? (Can we even safely do so, e.g. the non-root could be in the pub cache, could be a different project on the users' system etc. So maybe checking if we are in the examples dir is the only sane thing to do?)
Tests:
* Added unit tests in `test/general.shard/android/migrations/cmake_android_16k_pages_migration_test.dart`
