[ cleanup ] Remove redundant imports and some minor changes

[spcfox]

Description

1. Redundant imports have been removed, and some have been replaced with more specific ones (e.g. Core.Unify → Core.UnifyState). I did not change public imports because it would affect idris2api.

   Many SnocList imports were introduced in [ refactor ] ScopedSnocList: Preparing for the long jump (Phase 1) #3512 but are only used in [ refactor ] ScopedSnocList: Swap Scope on SnocList (Phase 2)  #3513. To simplify conflict resolution, I have moved them into a separate commit.

   Some public imports are not entirely clear in intent, so it may be worth reviewing them. For example:
   

   Idris2/src/Idris/Syntax.idr

   Lines 3 to 9 in 8c970f1

   	import public Core.Context
   	import public Core.Context.Log
   	import public Core.Core
   	import public Core.FC
   	import public Core.Normalise
   	import public Core.Options
   	import public Core.TT

   
   In any case, this is easier to address once unnecessary imports are removed, as missing dependencies will surface as errors.

2. Added public imports for modules that are always used together.

3. Minor cleanup of PPrint.

4. Removed %inline and rewrote Core.sequence. When inlined, it expands into a very large expression. The only reason why this wasn't discovered earlier is that this function isn't used. I didn't remove it because it will be useful when writing monadic code.

Self-check

I think cleaning up imports does not need to be added to the changelog.

• This is my first time contributing, I've carefully read CONTRIBUTING.md
  and I've updated CONTRIBUTORS.md with my name.
• If this is a fix, user-facing change, a compiler change, or a new paper
  implementation, I have updated CHANGELOG_NEXT.md