Adopt "pretty accessors" in MLIR

MLIR mainline added the ability to synthesize get/setters with a properly camel cased and get/set-prefixed name, see [this patch](https://reviews.llvm.org/D111033) and [this announcement](https://llvm.discourse.group/t/psa-ods-generated-accessors-will-change-to-have-a-get-prefix-update-you-apis/4476/2).

We should do a merge from MLIR mainline to get this, and then adopt it in the CIRCT dialects. I don't think we need to do the multistage adoption thing, we can just jump directly to `_Prefixed`

Start by reviewing the linked MLIR mainline patch and announcement, then inspect the CIRCT dialect definitions that use generated accessors. Merge the MLIR change and adopt the `_Prefixed` accessor behavior across CIRCT dialects; done means the dialects use the new get/set-prefixed, camel-cased accessors without requiring multistage adoption.

Written by the indexing model from the issue text.