[release/8.0] JIT: Handle mistyped commas in morph in pre-order too (#91718)

[release/8.0] JIT: Handle mistyped commas in morph in pre-order too (#91718)

* JIT: Compensate for mistyped commas in morph pre-order too

Morph has post-order logic to compensate for mistyped commas produced by
impStoreStruct. However, block morphing can optimize unused stores into
INDs; this interacts with the mistyped commas to produce illegal IR
shapes (e.g. `COMMA<simd12>(..., IND<ubyte>(...))`).

The ideal solution is to fix impStoreStruct (#91586 tracks this), but
this change has a more surgical fix for the problem that can be
backported to .NET 8.

Fix #91443

* Fix build

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Co-authored-by: Jakob Botsch Nielsen <jakob.botsch.nielsen@gmail.com>
Co-authored-by: Jeff Schwartz <jeffschw@microsoft.com>