Use a IntSet backed data structure instead of `UniqSet Unique`

Currently this is used in:

compiler/GHC/Builtin/Types.hs:cTupleTyConKeys :: UniqSet Unique
compiler/GHC/CmmToAsm/X86/Instr.hs: -> UniqSet Unique
compiler/GHC/Core/DataCon.hs: avoid_uniqs :: UniqSet Unique
compiler/GHC/Core/TyCon.hs:kindTyConKeys :: UniqSet Unique
compiler/GHC/HsToCore/Pmc/Solver.hs:triviallyInhabitedTyConKeys :: UniqSet Unique

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