Remove PostTypeChecker

[konnov]

Blocked by #1880.

Extracted from #1870, as it requires more work on the integration tests.

Closes #1323. Removed the PostTypeChecker pass, as it was really stepping in the way, producing incomprehensible error messages. This started to happen in conjunction with row types, which can be quite tricky to understand when they contain a free variable. This feature should have been implemented in a separate PR, but it was too late. Here are the affected files:

• deleted PostTypeCheckerPassImpl.scala

• added MonotypeLanguagePred that ensures that all types are monotypes

• placed an additional check with MonotypeLanguagePred in BoundedCheckerPassImpl

• added/changed a few additional classes ReTLACombinedPredicate.scala, ReTLAToVMTModule.scala.

• Ran make fmt-fix (or had formatting run automatically on all files edited)

• Entries added to ./unreleased/ for any new functionality

[codecov-commenter]

Codecov Report

Merging #1878 (fefec2d) into unstable (388d695) will decrease coverage by 0.08%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##           unstable    #1878      +/-   ##
============================================
- Coverage     76.75%   76.67%   -0.09%     
============================================
  Files           400      401       +1     
  Lines         12305    12319      +14     
  Branches        574      575       +1     
============================================
  Hits           9445     9445              
- Misses         2860     2874      +14     

Impacted Files	Coverage Δ
...syte/apalache/tla/bmcmt/config/CheckerModule.scala	0.00% <ø> (ø)
...ache/tla/bmcmt/config/ReTLACombinedPredicate.scala	0.00% <0.00%> (ø)
...e/apalache/tla/bmcmt/config/ReTLAToVMTModule.scala	0.00% <0.00%> (ø)
...ache/tla/bmcmt/passes/BoundedCheckerPassImpl.scala	0.00% <0.00%> (ø)
...che/tla/lir/transformations/LanguageWatchdog.scala	50.00% <0.00%> (ø)
...ransformations/standard/MonotypeLanguagePred.scala	0.00% <0.00%> (ø)
...a/at/forsyte/apalache/tla/lir/TlaLevelFinder.scala	97.36% <0.00%> (-2.64%)	⬇️
...he/io/annotations/parser/CommentPreprocessor.scala	97.80% <0.00%> (+1.09%)	⬆️

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[shonfeder]

Thank you for factoring out for a smaller review.

I'll wait to review here until the integration tests are passing.

[konnov]

This PR has passing tests. @Kukovec, @shonfeder, do you have free cycles to review this PR?