[interp] Implement tailcalls

[kg]

This PR currently implements tailcalls for CALL and CALLVIRT. The opcode for tail position calli is also generated but not implemented since it wasn't immediately obvious how to implement it (it doesn't look like the mono interpreter has an opcode for it.)

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[Copilot]

Pull Request Overview

This PR implements tailcall support for the CoreCLR interpreter, enabling proper tail call optimization for CALL and CALLVIRT operations. The implementation reuses the current stack frame for tail calls instead of creating a new one, which is essential for proper tail call semantics.

Key changes:

• Adds new tail call opcodes (INTOP_CALL_TAIL, INTOP_CALLVIRT_TAIL, INTOP_CALLI_TAIL)
• Implements tail call logic that reuses the current stack frame by copying arguments and reinitializing the frame
• Updates the InterpMethod structure to track argument size needed for tail call argument copying

Reviewed Changes

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

File	Description
src/coreclr/vm/interpexec.cpp	Implements tail call execution logic and adds isTailcall flag handling
src/coreclr/interpreter/intops.def	Defines new tail call opcodes
src/coreclr/interpreter/interpretershared.h	Adds argsSize field to InterpMethod for tail call argument copying
src/coreclr/interpreter/compiler.cpp	Updates compiler to emit tail call opcodes and pass argsSize to InterpMethod constructor

[kg]

Rebased and verified that tailcall.cmd still passes in InterpModes 1 and 2 (in addition to DOTNET_Interpreter=tailcall!*)