Ensure that we consistently copy otherRegs

[tannergooding]

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[Copilot]

Pull request overview

This PR extends the JIT’s “copy register assignment” helper logic to more consistently propagate multi-register (“otherRegs”) state across additional node kinds (locals, multireg ops, and JIT intrinsics), and adjusts some multireg handling in register-count/dump code to rely less on FEATURE_MULTIREG_RET compile-time gating.

Changes:

• Add CopyOtherRegs helpers for GenTreeLclVar, GenTreeMultiRegOp, and GenTreeJitIntrinsic.
• Update GenTree::CopyReg to copy multireg state for calls, multireg ops (32-bit), copy/reload nodes, HW intrinsics, and multireg locals.
• Refactor GenTree::GetRegisterDstCount, and make gtDispMultiRegCount / gtDispRegVal available under DEBUG without FEATURE_MULTIREG_RET gating.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/coreclr/jit/gentree.h	Adds CopyOtherRegs helpers on several node types to support multireg state propagation.
src/coreclr/jit/gentree.cpp	Extends CopyReg logic and refactors GetRegisterDstCount; adjusts debug dump helpers’ feature gating.
src/coreclr/jit/compiler.h	Removes FEATURE_MULTIREG_RET gating for gtDispMultiRegCount declaration under DEBUG.