Make atomics GenTreeIndir-derived

[SingleAccretion]

This is the first (zero-diff, hence quirks) part of fixing #92784.

We make all atomics OperIsIndir - they are a lot like stores and should share the common machinery like GTF_IND_NONFAULTING handling seamlessly this way.

[ghost]

Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch
See info in area-owners.md if you want to be subscribed.

Issue Details

---

This is the first (zero-diff, hence quirks) part of fixing #92784.

We make all atomics OperIsIndir - they are a lot like stores and should share the common machinery like GTF_IND_NONFAULTING handling.

There is a bit of a TP diff locally that looks like inlining noise.

Author:	SingleAccretion
Assignees:	-
Labels:	area-CodeGen-coreclr, community-contribution
Milestone:	-

[SingleAccretion]

@dotnet/jit-contrib

Diffs - none in code, as expected.

There is an anomalous TP regression on Windows x64; it is not yet clear why that is - it does not reproduce locally. I will need to pull the latest main and recheck, however, it may also be due to the difference in MSVC versions. In either case, I believe it to be due to some different inlining decisions.

Edit: I have confirmed the above. GenTree::OperRequiresCallFlag is no longer inlined into all of its callers because of the change in the opcode order (which, perhaps, makes MSVC's IR for it use a switch and be considered more complex...).