feat: tactic code actions framework

[digama0]

• depends on: feat: 'Try this' support #130
• depends on: feat: Hole commands #131

This implements a code action provider which uses the @[tactic_code_action] attribute to register code actions specifically on tactics and tactic sequences. The main purpose is to allow for having many code actions which all use the same syntax / info tree traversal setup.

This implementation is a bit sophisticated, because it wants to avoid calling tactic code actions for multiple overlapping tactics. It selects the innermost applicable tactic, or the space between tactics for tacticSeq code actions.

So far there are not many actual code actions implemented. A basic tactic code action added here is the Remove tactics after 'no goals' code action which removes a tactic which is called on no goals, and anything after it.