Allow compressed displacement to be used when profitable

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This should save 1-byte of encoding space as compared to using imm32, when applicable.

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Pull Request Overview

This PR adds logic in emitter::TakesEvexPrefix to detect when a memory displacement can be compressed to 8 bits via EVEX and only emits the prefix when profitable, saving encoding space.

• Compute stack or address displacement and check if it fits in a signed byte
• Call TryEvexCompressDisp8Byte for larger displacements and return true when compression succeeds

Comments suppressed due to low confidence (1)

src/coreclr/jit/emitxarch.cpp:1926

• No tests were added to verify the new compressed displacement logic (TryEvexCompressDisp8Byte); consider adding unit tests covering both compressible and non-compressible displacement cases to ensure correct behavior.

            dsp = TryEvexCompressDisp8Byte(id, dsp, &dspInByte);