JIT: support strength reducing multiple IVs with different step values provided they have a gcd > 1

[jakobbotsch]

Strength reduction should still be profitable in these cases.

Suggested by @AndyAyersMS here: #104243 (comment)

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[jakobbotsch]

One interesting canonical loop shape we can target is the one in #102068 (comment).

[jakobbotsch]

Another case is the loop-cloned delegate GDV version of System.Linq.Enumerable+EnumerableSorter`2[System.__Canon,System.Decimal]:ComputeKeys(System.__Canon[],int):this (Tier1) in benchmarks.run_pgo:

       mov      rdx, 0xD1FFAB1E      ; code for LinqBenchmarks+<>c:<Order00LinqMethodX>b__17_0(Product):System.Decimal:this
       cmp      qword ptr [rbp+0x18], rdx
       jne      SHORT G_M57524_IG10
       cmp      dword ptr [rbx+0x08], r13d
       jl       SHORT G_M57524_IG10
						;; size=40 bbWeight=0.99 PerfScore 10.61
G_M57524_IG05:        ; bbWeight=76.18, gcrefRegs=4048 {rbx rsi r14}, byrefRegs=0000 {}, byref, isz
       ; gcrRegs -[rbp]
       mov      edx, r15d
       mov      r8, gword ptr [rbx+8*rdx+0x10]
       ; gcrRegs +[r8]
       vmovups  xmm0, xmmword ptr [r8+0x20]
       vmovups  xmmword ptr [rsp+0x28], xmm0
       shl      rdx, 4
       vmovups  xmm0, xmmword ptr [rsp+0x28]
       vmovups  xmmword ptr [r14+rdx+0x10], xmm0
       inc      r15d
       cmp      r13d, r15d
       jg       SHORT G_M57524_IG05

The IV is r15d and we skip strength reduction:

  Advancing cursors to be 2-derived
    [0] [000119]: <L01, 0, 8>
    [1] [000136]: <L01, 0, 16>
    [1] does not match; will not advance

But we could strength reduce the 8-step IV and rephrase the 16 step one in terms of it.