Optimize more bound checks around logical operators

[EgorBo]

Closes #122150
Example:

int Test(byte inData)
{
    ReadOnlySpan<byte> base64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="u8;
    return base64[((inData & 0x03) << 4) | ((inData & 0xf0) >> 4)];
}

Was:

; Method Program:Test(byte):int:this (FullOpts)
       sub      rsp, 40
       movzx    rax, dl
       mov      ecx, eax
       and      ecx, 3
       shl      ecx, 4
       and      eax, 240
       sar      eax, 4
       or       eax, ecx
       cmp      eax, 65
       jae      SHORT G_M54716_IG04
       mov      rcx, 0x196B4CC2D88      ; static handle
       movzx    rax, byte  ptr [rcx+rax]
       add      rsp, 40
       ret      
G_M54716_IG04:
       call     CORINFO_HELP_RNGCHKFAIL
       int3     
; Total bytes of code: 55

Now:

; Method Program:Test(byte):int:this (FullOpts)
       movzx    rax, dl
       mov      ecx, eax
       and      ecx, 3
       shl      ecx, 4
       and      eax, 240
       sar      eax, 4
       or       eax, ecx
       mov      rcx, 0x171D74A2D88      ; static handle
       movzx    rax, byte  ptr [rcx+rax]
       ret      
; Total bytes of code: 36

As the result, was able to optimize bound checks in Convert.ConvertToBase64Array

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[EgorBo]

@MihuBot

[am11]

Can we remove unsafe from ConvertToBase64Array's two callers?