Use cached uniques for maps over TyCons and some other things.

Closed Andreas Klebinger requested to merge wip/andreask/tyConEnv into master

The main idea is to avoid the indirection of Foo->Name->Unique and instead going Foo->Unique for certain lookups and membership tests.

There are still places where we can apply this pattern and some cleanup to do.

We introduce a few new map synonyms for this (TyConEnv/TyConSet) or use UniqFM/UniqueSet depending on context.

Edited by Andreas Klebinger

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