JIT: Avoid creating impossible equality assertions

[jakobbotsch]

Fix #113940

[Copilot]

Pull Request Overview

This PR fixes issue #113940 by preventing the creation of impossible equality assertions in the JIT compiler's assertion propagation optimization. The fix addresses cases where a small local variable (like byte or short) would be compared to a constant value outside its valid range, which would create impossible assertions that could cause problems elsewhere in the compiler.

• Adds validation to detect when a truncated constant value differs from the original value for small local variables
• Avoids creating assertions for impossible equality comparisons that indicate unreachable code
• Maintains existing behavior for store operations while fixing the issue for other operations

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[jakobbotsch]

cc @dotnet/jit-contrib PTAL @EgorBo

[EgorBo]

LGTM

[jakobbotsch]

No diffs