Introduce a new derivation mechanism supporting GADTs

[lsrcz]

A lot of changes has been done in this pull request. Notably:

• The deriveGADT template haskell procedure now derive all relevant instances for GADTs, and the old TH derivation mechanism has been removed.
• Added EvalModeConvertible for a unified constraint for the evaluation modes that can be converted to each other with ToCon and ToSym.
• We no longer support direct toCon from a union to a single value or toSym from a single value to a union. These should now be done through mrgToSym, toUnionSym, and unionToCon.
• Changed the EvalMode tag for Con to C and Sym to S.
• Fixed some missing constraints for unified interfaces.
• Fixed badly staged types in the lifting of terms.
• Fixed the Read instance for bit-vectors on GHC 9.12.

[codecov]

Codecov Report

Attention: Patch coverage is 42.72959% with 898 lines in your changes missing coverage. Please review.

Project coverage is 75.23%. Comparing base (14f4c81) to head (d109fdb).
Report is 63 commits behind head on main.

Files with missing lines	Patch %	Lines
...e/Internal/Internal/Impl/Core/Data/Class/PPrint.hs	11.94%	96 Missing and 22 partials ⚠️
...nternal/Internal/Impl/Core/Data/Class/Mergeable.hs	43.87%	78 Missing and 9 partials ⚠️
...Internal/Internal/Impl/Core/Control/Monad/Union.hs	49.38%	68 Missing and 14 partials ⚠️
...e/Internal/Internal/Decl/Core/Data/Class/PPrint.hs	44.28%	43 Missing and 35 partials ⚠️
...ternal/Internal/Impl/Core/Data/Class/ExtractSym.hs	12.34%	54 Missing and 17 partials ⚠️
.../Internal/Internal/Impl/Core/Data/Class/EvalSym.hs	30.66%	41 Missing and 11 partials ⚠️
...l/Internal/Impl/Core/Data/Class/SimpleMergeable.hs	57.72%	50 Missing and 2 partials ⚠️
...e/Internal/Internal/Decl/Core/Data/Class/Solver.hs	20.63%	47 Missing and 3 partials ⚠️
...nternal/Internal/Decl/Core/Data/Class/Mergeable.hs	60.86%	27 Missing and 9 partials ⚠️
...te/Internal/Internal/Decl/Core/Data/Class/SymEq.hs	18.18%	20 Missing and 7 partials ⚠️
... and 16 more

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #267       +/-   ##
===========================================
+ Coverage   54.65%   75.23%   +20.57%     
===========================================
  Files         122      209       +87     
  Lines       12936    30947    +18011     
  Branches      906     2189     +1283     
===========================================
+ Hits         7070    23282    +16212     
- Misses       4960     5476      +516     
- Partials      906     2189     +1283     

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