Mitosis does not always accurately delete old files

[samijaber]

Ran into a tricky bug the other day. Had a file src/helpers/foo.ts, and moved it to src/helpers/foo/index.ts to be able to add helpers. Unfortunately, the clean() function will only delete outputs that match the current list of existing files. Since there was no longer a src/helpers/foo.ts, clean() did not attempt to delete it.

We don't want to blindly delete the entire output dir. We have cases where we have files there that need to stay, such as a dist/package.json, etc.

https://github.com/BuilderIO/mitosis/blob/main/packages/cli/src/build/build.ts#L94-L102