nir/print: add support for print annotations

nir/print: add support for print annotations

Caller can pass a hashtable mapping NIR object (currently instr or var,
but I guess others could be added as needed) to annotation msg to print
inline with the shader dump.  As the annotation msg is printed, it is
removed from the hashtable to give the caller a way to know about any
unassociated msgs.

This is used in the next patch, for nir_validate to try to associate
error msgs to nir_print dump.

Signed-off-by: Rob Clark <robclark@freedesktop.org>
Reviewed-by: Eduardo Lima Mitev <elima@igalia.com>
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>