Arm AdvSimd: Rename StoreVectorMxN to Store

[SwapnilGaikwad]

Partially (item 3) fixes: #102340

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[SwapnilGaikwad]

Hi @kunalspathak , this addresses the final (item 3) from #102340.
Didn't change mono bits.

@a74nh

[kunalspathak]

Added few comments.

[kunalspathak]

@SwapnilGaikwad - it seems there are some test failures:

Assert failure(PID 85467 [0x00014ddb], Thread: 2420517 [0x24ef25]): Assertion failed '!HWIntrinsicInfo::IsInvalidNodeId(intrinsicId)' in 'JIT.HardwareIntrinsics.Arm._AdvSimd.Storex2SByteTest:RunBasicScenario_UnsafeRead():this' during 'Importation' (IL size 112; hash 0x4100adc6; MinOpts)

    File: /Users/runner/work/1/s/src/coreclr/jit/gentree.cpp:28149
    Image: /private/tmp/helix/working/A1D908D4/p/corerun

[fanyang-mono]

Test AdvSimd_r.dll passed locally

Supported ISAs:
  AdvSimd:   True
  Aes:       True
  ArmBase:   True
  Crc32:     True
  Dp:        False
  Rdm:       False
  Sha1:      True
  Sha256:    True
  Sve:       False

...

Expected: 100
Actual: 100
END EXECUTION - PASSED

[fanyang-mono]

Mono change is good and complete.

[kunalspathak]

coreclr LGTM.

[kunalspathak]

/ba-g the only failure on windows/x64 is unrelated and seems flaky