Jade authored Mar 28, 2024 and Marge Bot committed May 15, 2024

- When suggesting Language extensions, also suggest Extensions which imply them
- Suggest ExplicitForAll and GADTSyntax instead of more specific
  extensions
- Rephrase suggestion to include the term 'Extension'
- Also moves some flag specific definitions out of Session.hs into
Flags.hs (#24478)

Fixes: #24477
Fixes: #24448
Fixes: #10893