Suggest using new Alligator GC

In some cases, we can suggest using new Garbage collector starting from GHC-8.10 (e.g. if we detect web-server dependencies or game programming deps). Or, simply, we can suggest using it always if the library builds with GHC-8.10 :slightly_smiling_face:

No files, tests, or entry points are named. Start by locating how Stan identifies the GHC version, library dependencies, and build compatibility, then determine whether Alligator GC should be suggested for web-server or game dependencies or for every library compatible with GHC-8.10. Done means the recommendation policy is decided and covered by tests.

Written by the indexing model from the issue text.