Don't panic on 'no skolem info' and add failing tests

We instead print a big ugly warning so that the user reports a bug:

WARNING:
  No skolem info - we could not find the origin of the following variables [a_aws[sk:1]]
  This should not happen, please report it as a bug following the instructions at:
  https://gitlab.haskell.org/ghc/ghc/wikis/report-a-bug
  Call stack:
      CallStack (from HasCallStack):
        pprTraceUserWarning, called at compiler/GHC/Tc/Errors.hs:2982:7 in ghc:GHC.Tc.Errors
T10949.hs:6:13: error:
    • Found hole: _ :: a
      Where: ‘a’ is a (rigid, skolem) type variable
               of unknown origin
               bound at T10949.hs:5:1-11
    • In the Template Haskell quotation [|| _ ||]
      In the expression: [|| _ ||]
      In the Template Haskell splice $$([|| _ ||])
    • Relevant bindings include
        x :: a (bound at T10949.hs:6:3)
        m :: a -> a (bound at T10949.hs:6:1)
      Valid hole fits include x :: a (bound at T10949.hs:6:3)
  |
6 | m x = $$([||_||])
  |             ^

Also improved the error message of unknown skolems a bit, including the definition SrcSpan.

Adds expect_broken tests for #19752 (closed), #20063 (closed), #19760 (closed), #19482 (closed), #10946 (closed)

Also adds a test for #16135 which is broken with debugged compilers.