Add missing interpreter HFA helpers

[janvorli]

There are missing helpers for 2, 3 and 4 vector64 and vector128 HFA in the interpreter call stubs.

This change implements them.

[Copilot]

Pull Request Overview

This PR adds missing interpreter HFA (Homogeneous Floating-point Aggregate) helpers for ARM64 to support returning 2, 3, and 4 element Vector64 and Vector128 structures. Previously, only single-element vector returns were implemented for the interpreter call stubs.

Key Changes:

• Added new return type enum values for multi-element Vector64/Vector128 HFAs
• Implemented corresponding interpreter stub functions and jitted method call helpers
• Extended return type detection logic to map HFA sizes to appropriate return types

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/coreclr/vm/callstubgenerator.h	Adds enum values for 2/3/4 element Vector64 and Vector128 return types
src/coreclr/vm/callstubgenerator.cpp	Adds function declarations, switch case handlers, and size-based return type detection for new HFA types
src/coreclr/vm/arm64/asmhelpers.asm	Implements ARM64 assembly stubs for new interpreter and jitted method return type handlers (Windows syntax)
src/coreclr/vm/arm64/asmhelpers.S	Implements ARM64 assembly stubs for new interpreter and jitted method return type handlers (Unix syntax)