Plugins don't use --local-engine framework on macOS/iOS #132228
Description
STR:
- Add new plugin API to the engine for iOS or macOS
- Build the engine
- Add use of the new API in a plugin, locally, for testing
- Try to run the plugin's example with
--local-engine
Compilation will fail, because podhelper.rb is unconditionally using the actual tool cache dir here and here. It looks like this regressed in #59044 and #72020; prior to those, we were using FLUTTER_FRAMEWORK_DIR, which the tool used to set to point to the local engine build.
This makes testing plugin API changes much harder than it used to be since it requires modifying flutter in some way.