Drop generic type constraints from Unsafe.BitCast

[MihaZupan]

Fixes #99205
Fixes #99006

MihuBot/runtime-utils#354

Most diffs appear to be more inlining / removing unreachable branches. For example seeing that these IndexOf* calls are passing in 0 and therefore deleting the checks and unreachable calls to PackedSpanHelpers

runtime/src/libraries/System.Net.Http/src/System/Net/Http/Headers/UriHeaderParser.cs

Lines 65 to 67 in 3462976

	int possibleUtf8Pos = input.AsSpan().IndexOfAnyExceptInRange((char)0, (char)127);
	if (possibleUtf8Pos >= 0 &&
	!input.AsSpan(possibleUtf8Pos).ContainsAnyExceptInRange((char)0, (char)255))

Part of the diff

 G_M22867_IG04:
-       xor      edx, edx
-       mov      dword ptr [rbp-0x2C], edx
-       mov      dword ptr [rbp-0x30], 127
-       movzx    rsi, word  ptr [rbp-0x2C]
-       movzx    rdx, word  ptr [rbp-0x30]
-       lea      r8d, [rsi-0x01]
-       cmp      r8d, 254
-       jae      SHORT G_M22867_IG05
-       lea      r8d, [rdx-0x01]
-       cmp      r8d, 254
-       jae      SHORT G_M22867_IG05
-       cmp      edx, esi
-       jl       SHORT G_M22867_IG05
-       sub      edx, esi
-       movsx    rdx, dx
-       movsx    rsi, si
-       mov      rdi, rax
-       mov      rax, 0xD1FFAB1E      ; code for System.PackedSpanHelpers:IndexOfAnyInRange[System.SpanHelpers+Negate`1[short]](byref,short,short,int):int
-       call     [rax]System.PackedSpanHelpers:IndexOfAnyInRange[System.SpanHelpers+Negate`1[short]](byref,short,short,int):int
-       jmp      SHORT G_M22867_IG06
-						;; size=77 bbWeight=1 PerfScore 15.25
-G_M22867_IG05:
-       mov      rdi, rax
+       mov      rdi, rcx
+       mov      ecx, esi
+       xor      esi, esi
+       mov      edx, 127
        mov      rax, 0xD1FFAB1E      ; code for System.SpanHelpers:NonPackedIndexOfAnyInRangeUnsignedNumber[ushort,System.SpanHelpers+Negate`1[ushort]](byref,ushort,ushort,int):int
        call     [rax]System.SpanHelpers:NonPackedIndexOfAnyInRangeUnsignedNumber[ushort,System.SpanHelpers+Negate`1[ushort]](byref,ushort,ushort,int):int

[dotnet-issue-labeler]

Note regarding the new-api-needs-documentation label:

This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.

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[jkotas]

LGTM!

[jakobbotsch]

FYI @dotnet/jit-contrib (JIT-EE GUID changed)

[tannergooding]

Sorry, I had thought jit-contrib had already been tagged above but now I see the area tag ended up being CompilerServices instead.

[LoopedBard3]

Another potentially related regression issue @MihaZupan
Windows x64: dotnet/perf-autofiling-issues#33044 (Only the IndexOfAny test)