Move [PAC] into a new MI field addr_flags
    
    Add a new print_pc which prints both the PC and a new field addr_flags.
    Call this wherever the PC is printed in stack.c.
    
    Add a new gdbarch method get_pc_address_flags to obtain the addr_flag
    contents. By default returns an empty string, on AArch64 this returns
    PAC if the address has been masked in the frame.
    
    Document this in the manual and NEWS file.
    
    gdb/ChangeLog:
    
    	* NEWS (Other MI changes): New subsection.
    	* aarch64-tdep.c (aarch64_get_pc_address_flags): New function.
    	(aarch64_gdbarch_init): Add aarch64_get_pc_address_flags.
    	* arch-utils.c (default_get_pc_address_flags): New function.
    	* arch-utils.h (default_get_pc_address_flags): New declaration.
    	* gdbarch.sh: Add get_pc_address_flags.
    	* gdbarch.c: Regenerate.
    	* gdbarch.h: Likewise.
    	* stack.c (print_pc): New function.
    	(print_frame_info) (print_frame): Call print_pc.
    
    gdb/doc/ChangeLog:
    
    	* gdb.texinfo (AArch64 Pointer Authentication)
    	(GDB/MI Breakpoint Information) (Frame Information): Document
    	addr_field.