Fix unnecessary bounds check with ulong index

[EgorBo]

Closes #76198

string Test(ulong ulValue, string[] names)
{
    if (ulValue < (ulong)names.Length)
        return names[(uint)ulValue];
    return null;
}

Codegen diff:

; Method Prog:Test(ulong,System.String[]):System.String:this (FullOpts)
       sub      rsp, 40
       mov      eax, dword ptr [r8+0x08]
-      mov      ecx, eax
-      cmp      rcx, rdx
+      cmp      rax, rdx
       jbe      SHORT G_M5198_IG05
-      cmp      edx, eax
-      jae      SHORT G_M5198_IG07
       mov      eax, edx
       mov      rax, gword ptr [r8+8*rax+0x10]
       add      rsp, 40
       ret      
G_M5198_IG05:
       xor      rax, rax
       add      rsp, 40
       ret      
-G_M5198_IG07:
-      call     CORINFO_HELP_RNGCHKFAIL
-      int3     
-; Total bytes of code: 44
+; Total bytes of code: 32

[EgorBo]

PTAL @AndyAyersMS @dotnet/jit-contrib

Very few diffs, but afair, @stephentoub had to use unsafe to workaround it.

the idea that (ulong)i < (ulong)arr.Length creates an assertion that i is less than arr.Length (unsigned) - basically, the same assertion that we generate for (uint)i < (uint)arr.Length today, I even re-used the same path

[AndyAyersMS]

Can you update the function header comment too?

[EgorBo]

Can you update the function header comment too?

Done

Failure is #101721