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`
Android 15 support 16k page sizes, it need [enable 16kb elf alignment](https://developer.android.com/guide/practices/page-sizes#compile-r26-lower).
the current plugin_ffi template will have below error if run on android 15 16k emulator
```
Failed to load dynamic library 'libffigen_app.so': dlopen
failed: empty/missing
DT_HASH/DT_GNU_HASH in
"/data/app/~~Ixsgxu2mj5fKxP1cXpjV6Q==/com.example.ffigen_app_example-6d_efR__WGu
4dsF4tLIaHw==/lib/arm64/libffigen_app.so"
(new hash type from the future?)
```
* Building shared C source code as part of the native build for platforms Android, iOS, Linux desktop, MacOS desktop, and Windows desktop.
* Sample code doing a synchronous FFI call.
* Sample code doing a long running synchronous FFI call on a helper isolate.
* Use of `package:ffigen` to generate the bindings.
