Update conservative value numbers during CSE

[JosephTremoulet]

When a CSE candidate's defs all share the same conservative value number,
its uses can be updated to share that conservative value number as well
when CSE is performed, because we are removing any reloads that may have
been the cause of the divergence. Performing this update can improve
subsequent range check elimination when the CSE use is array length or
index in a bounds check.

[JosephTremoulet]

@dotnet/jit-contrib PTAL; I implemented @mikedn's suggestion from #5371. It gets the related (straight-line) case in #9097; it doesn't get the original (loop) case from #5371, but is an incremental step in the right direction nonetheless.

Diffs are a bunch of removed bounds checks and null checks.

SPMI asm diffs report 0.83% codesize improvement across 6474 affected methods, jit-analyze summary as follows:

Summary:
(Note: Lower is better)

Total bytes of diff: -4882 (0.00 % of base)
    diff is an improvement.

Total byte diff includes 0 bytes from reconciling methods
        Base had    0 unique methods,        0 unique bytes
        Diff had    0 unique methods,        0 unique bytes

Top file improvements by size (bytes):
       -1196 : dasmset_1\diff\Methodical\fp\exgen\10w5d_cs_do\10w5d_cs_do.dasm (-0.13 % of base)
       -1195 : dasmset_1\diff\Methodical\fp\exgen\10w5d_cs_ro\10w5d_cs_ro.dasm (-0.14 % of base)
        -925 : dasmset_1\diff\System.Private.CoreLib.dasm (-0.03 % of base)
        -167 : dasmset_1\diff\System.Linq.Parallel.dasm (-0.03 % of base)
        -162 : dasmset_1\diff\Microsoft.CSharp.dasm (-0.04 % of base)

65 total files with size differences (65 improved, 0 regressed).

Top method improvements by size (bytes):
         -63 : dasmset_1\diff\System.Private.CoreLib.dasm - System.Globalization.CultureData:get_SENGDISPLAYNAME():ref:this
         -61 : dasmset_1\diff\System.Reflection.Metadata.dasm - System.Reflection.PortableExecutable.PEReader:GetPESectionBlock(int):ref:this
         -56 : dasmset_1\diff\System.Linq.Parallel.dasm - System.Linq.Parallel.FixedMaxHeap`1[Int32][System.Int32]:HeapifyRoot():this
         -52 : dasmset_1\diff\System.Private.CoreLib.dasm - System.Globalization.DateTimeFormatInfo:get_DateTimeOffsetPattern():ref:this
         -49 : dasmset_1\diff\Methodical\fp\exgen\10w5d_cs_do\10w5d_cs_do.dasm - testout1:Func_0_1_1_2_1():double

466 total methods with size differences (466 improved, 0 regressed).

[pgavlin]

LGTM

[briansull]

LGTM,
I think these are some of the same range checks that we get if we re-run value numbering a second time after we do the CSE phase...