Ensure that folding of unary mask operations doesn't modify the tracked op2

[tannergooding]

This resolves #117378

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[Copilot]

Pull Request Overview

This PR refactors the JIT’s unary mask folding to preserve the original second operand and adds a regression test reproducing the issue (fixes #117378).

• Adjust gtFoldExprHWIntrinsic to use effectiveOper and avoid mutating op2 directly.
• Add a new JIT regression test project and C# test to trigger the assertion.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/coreclr/jit/gentree.cpp	Refactored mask-folding logic to handle GT_NOT without modifying op2
src/tests/JIT/Regression/JitBlue/Runtime_117377/Runtime_117377.csproj	Added new test project
src/tests/JIT/Regression/JitBlue/Runtime_117377/Runtime_117377.cs	Added generated test case calling the problematic intrinsic code

Comments suppressed due to low confidence (2)

src/tests/JIT/Regression/JitBlue/Runtime_117377/Runtime_117377.csproj:3

• The project file is missing a element, so it won’t build. Add something like net8.0 inside the PropertyGroup to match other JIT tests.

    <Optimize>True</Optimize>

src/tests/JIT/Regression/JitBlue/Runtime_117377/Runtime_117377.cs:32

• To ensure this method isn’t inlined (and thus triggers the intended JIT folding path), add [MethodImpl(MethodImplOptions.NoInlining)] above M4. Remember to import System.Runtime.CompilerServices.

        public byte M4()

[amanasifkhalid]

LGTM, thanks!

[tannergooding]

/ba-g unrelated timeouts/failures