Introduce triton-ptr-to-memref pass

[nhat-nguyen]

This PR introduces the triton-ptr-to-memref pass responsible for converting function signature that uses triton ptr to use memref instead. This is part of the work to allow triton-shared to lower gather / scatter pointer sequences.

Intended lowering pipeline:

• triton-to-structured (no changes):
  • analyzes structured addptr sequences
    • introduces tts.make_tptr %ptr_arg with offsets and strides
    • introduces tts.load and tts.store
  • leaves unstructured addptr sequences and their corresponding tt.load and tt.store intact
• fold-unstructured-ptr (PR here):
  • converts all unstructured addptr sequences into sequences that compute pointer offsets
    • introduces tts.make_unstructured_tptr %ptr_arg %offsets
  • removes all tt.addptr
• structured-to-memref (to be updated in a different PR):
  • currently converts everything to memref including scalar addptr and kernel arguments
  • will change to just convert ops in the tts dialect to memref with the exception of tts.make_unstructured_tptr
• unstructured-to-memref (to be introduced in a different PR):
  • converts the remaining unstructured tt.load, tt.store, and tts.make_unstructured_tptr into memref
• triton-ptr-to-memref (this PR):
  • converts kernel arguments with pointer type to memref