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	Fix an interaction between zonking of Insts and GADTs
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Insts float outwards, perhaps out of the scope of a type-refining GADT case.
So we have to make sure they are fully zonked wrt the type refinement.

tcSimplifyCheck does this, but there were two omissions
a) the tcInstStupidTheta in TcPat.tcConPat didn't get zonked
b) a Dict and Lit Inst contained an Id that wasn't zonked, to save work

To fix (b), Insts have a little less cached info; the Name is held instead
of the Id, so that the Id doesn't need to be zonked.

One test in typecheck/should_compile/tc182