[xray][AArch64] Rewrite trampoline

Optimize (cmp+beq => cbz), duduplicate code (SAVE_REGISTERS/RESTORE_REGISTERS),
improve portability (use ASM_SYMBOL to be compatible with Mach-O), and fix style
issues.
Also, port D37965 (x86 tail call) to __xray_FunctionTailExit.