[release/8.0-rc2] Don't generate AddMask as it requires more explicit consideration of semantics

[github-actions]

Backport of #92282 to release/8.0-rc2

/cc @tannergooding

Customer Impact

The customer will experience incorrect codegen that results in the code doing something different than they intended when summing Vector512<T>s created via certain patterns with operator+. Customer reported in #92261.

Testing

Manual validation that the reported customer scenario produces the expected codegen.

Risk

Low. This is simply removing an optimization that shouldn't have been included in the first place as it was incomplete. Additional work was required to ensure that the kadd code generation worked as expected for adding two masks together.

[ghost]

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

Issue Details

---

Backport of #92282 to release/8.0

/cc @tannergooding

Customer Impact

Testing

Risk

IMPORTANT: If this backport is for a servicing release, please verify that:

• The PR target branch is release/X.0-staging, not release/X.0.

• If the change touches code that ships in a NuGet package, you have added the necessary package authoring and gotten it explicitly reviewed.

Author:	github-actions[bot]
Assignees:	-
Labels:	area-CodeGen-coreclr
Milestone:	-

[carlossanlop]

@tannergooding is it your intention to target RC2? There's still time. The hard due date for merging is on Sept 24th. If yes, then you need to retarget your PR to release/8.0-rc2 and you need Tactics approval for merging. Once merged, the bot will automatically flow your change to the base release/8.0 branch for you.

cc @jeffhandley @artl93

[tannergooding]

This is a JIT side issue, so it likely needs determination from @JulieLeeMSFT or @jakobbotsch

Given it's a correctness issue, it might be better to target RC2

[jakobbotsch]

Agreed, let's target rc2 for this one since it's customer reported.

[jeffschwMSFT]

please get a code review

[carlossanlop]

Approved by Tactics via email.

The RC2 branch had a generalized failure for which we just merged a fix, so I updated this PR to ensure the CI is clean.