Flutter tool should only create its own files in a .flutter directory #105374
Description
Use case
My team uses a monorepo, and we use VSCode devcontainers for the backend and also for. The devcontainer version of flutter is constantly fighting with the system version of flutter over .flutter-plugins, and .flutter-plugins-dependencies. This isn't an issue with .dart_tool, because I can mount a volume there in the VSCode devcontainer so the two don't fight.
Proposal
It would be simpler for my use case (and many others) to simply have flutter place all of its generated system-dependent configuration inside a .flutter directory, matching the behavior of dart and most other CLI tools. This would also make it easier to maintain .gitignore files.
EDIT: Mistakenly also included .packages in this list, but that seems to already be fixed with #99677