Ensure that GT_CNS_VEC is handled in LinearScan::isMatchingConstant

[tannergooding]

This is a small follow up to #68874 but provides decent improvements, particularly where the same constant (Zero and AllBitsSet in particular) is repeatedly used.

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Issue Details

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This is a small follow up to #68874 but provides decent improvements, particularly where the same constant (Zero and AllBitsSet in particular) is repeatedly used.

Author:	tannergooding
Assignees:	-
Labels:	area-CodeGen-coreclr
Milestone:	-

[TIHan]

Looks good and easy change.

[tannergooding]

Example diffs

Note that ymm7 is set to "all bits set" first, and then reused on the last line rather than also using ymm6

 vpcmpeqd ymm7, ymm7, ymm7
vxorps ymm6, ymm7, ymm6
vcmpps ymm4, ymm4, ymm0, 0
vorps ymm4, ymm4, ymm6
- vpcmpeqd ymm6, ymm6, ymm6- vpcmpeqd ymm4, ymm4, ymm6+ vpcmpeqd ymm4, ymm4, ymm7

Note how ymm2 isn't reloaded with reloc @RDW00 because it was already in ymm2:

 vmovupd ymm2, ymmword ptr[reloc @RWD00]
vpshufb ymm0, ymm0, ymm2
vperm2i128 ymm0, ymm0, ymm0, 1
- vmovupd ymm2, ymmword ptr[reloc @RWD00]
vpshufb ymm1, ymm1, ymm2

[tannergooding]

Noting ARM64 already had a path here since it needed special handling for Zero and AllBitsSet, it just wasn't getting used in LSRA

[tannergooding]

@kunalspathak could you take a look? Its super small (8 lines) but touches LSRA so I'd appreciate your sign-off as well.

[kunalspathak]

LGTM