[XLA:GPU] Extract and generalize fusion-related logic from compiler...

[XLA:GPU] Extract and generalize fusion-related logic from compiler pass-specific classes: LayoutsAreReduceInputFusionFriendly

This is the first of a series of CLs. The idea is to extract and generalize IsFusable... logic scattered across GpuInstructionFusion, FusionMerger, and GpuMultiOutputFusion into the joint util. Eventually, functions like LayoutsAreReduceInputFusionFriendly will no longer be directly exposed, but rather used internally to determine fusibility of given ops.

PiperOrigin-RevId: 210888913