For historical reasons, the flutter tool uploads dill files to paths based on the entrypoint URI. This isn't actually necessary, and the tool can use specific files : main.dart.incremental.dill for incremental dills, and main.dart.dill/main.dart.swap.dill for full dills. This allows hot restarting applications with an entrypoint outside of lib/ and simplifies the devFS code.

Fixes #63243