Rollup merge of #143271 - cjgillot:gvn-types, r=oli-obk

Store the type of each GVN value

MIR is fully typed, so type information is an integral part of what defines a value. GVN currently tries to circumvent storing types, which creates all sorts of complexities.

This PR stores the type along with the enum `Value` when defining a value index. This allows to simplify a lot of code.

Fixes rust-lang/rust#128094
Fixes rust-lang/rust#135128

r? ``````@ghost`````` for perf

Author: matthiaskrgr