Make reinterpret specialize fully. (#50670)
Fixes https://github.com/JuliaLang/julia/issues/50612
The issue here was the reinterpret change made a bunch of operations
like `Core.bitcast(UInt64,24)` not fold, even though they are fully
known at compile time. That made `UInt32(Char)` not inline which then
caused the regression.
