Adds a new repo tooling command that removes dev_dependencies, which
aren't needed to consume a package, only for development. Also adds
a --lib-only flag to analyze to analyze only the client-facing code.
This is intended for use in the legacy analyze CI steps, primarily to
solve the problem that currently plugins that use Pigeon can't support a
version of Flutter older than the version supported by Pigeon, because
otherwise the legacy analysis CI steps fail.

Adds this new command to the legacy analysis CI step, and restores
the recently-removed 2.8/2.10 compatibility to path_provider.