Optimize JTRUE(cast_helper EQ/NE null) expansion

[EgorBo]

Slightly optimize cast expansion when the actual result is used inside "NE/EQ 0" ("is instance" pattern). This improvement is motivated by the comment https://devblogs.microsoft.com/dotnet/performance-improvements-in-net-9/?commentid=21225#comment-21225

public bool Test()
{
    if (_obj is B)
        return true;
    return false;
}

Current codegen:

; Assembly listing for method Tests:Test():ubyte:this (Tier1)
G_M39947_IG01:
       sub      rsp, 40
G_M39947_IG02:
       mov      rdx, gword ptr [rcx+0x08]
       mov      rax, rdx
       test     rax, rax
       je       SHORT G_M39947_IG05
G_M39947_IG03:
       mov      rcx, 0x7FFC7909C970      ; Tests+C
       cmp      qword ptr [rax], rcx
       je       SHORT G_M39947_IG05
G_M39947_IG04:
       mov      rcx, 0x7FFC7909C7F8      ; Tests+B
       call     CORINFO_HELP_ISINSTANCEOFCLASS
G_M39947_IG05:
       test     rax, rax    ;; <-- we can duplicate this tail into return true/return false tails.
       setne    al
       movzx    rax, al
G_M39947_IG06:
       add      rsp, 40
       ret
; Total bytes of code 60

New codegen:

; Assembly listing for method Tests:Test():ubyte:this (Tier1)
G_M39947_IG01:
       sub      rsp, 40
G_M39947_IG02:
       mov      rdx, gword ptr [rcx+0x08]
       mov      rax, rdx
       test     rax, rax
       je       SHORT G_M39947_IG07
G_M39947_IG03:
       mov      rcx, 0x7FFC7909C970      ; Tests+C
       cmp      qword ptr [rax], rcx
       je       SHORT G_M39947_IG05
G_M39947_IG04:
       mov      rcx, 0x7FFC7909C7F8      ; Tests+B
       call     CORINFO_HELP_ISINSTANCEOFCLASS
       test     rax, rax
       je       SHORT G_M39947_IG07
G_M39947_IG05:
       mov      eax, 1
G_M39947_IG06:
       add      rsp, 40
       ret
G_M39947_IG07:
       xor      eax, eax
G_M39947_IG08:
       add      rsp, 40
       ret
; Total bytes of code 68

Diff: https://www.diffchecker.com/swl6knBa/
(slightly bigger size in this case due to duplicated epilogue, but no more extra "is zero" check)

PS: this PR needs #107499 to handle return obj is X; like patterns.

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[EgorBo]

/azp run runtime-coreclr pgo

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[EgorBo]

/azp run runtime-coreclr pgo

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