[llvm] [CodeGen] change prototype of RegClassFilterFunc (PR #93525)

[Christudasan Devadasan via llvm-commits]

cdevadas wrote:

The filtering is now more on the Registers itself than the regclass; hence, the following changes make more sense. If everyone thinks it is a good idea, I can change it.
RegClassFilterFunc -> RegAllocFilterFunc
ShouldAllocateClass -> ShouldAllocateRegister

https://github.com/llvm/llvm-project/pull/93525