test/utils: support operator name aliases

test/utils: support operator name aliases

Previously there was a flat list of operators (pixman_op_t), used to
iterate over all operators when looking up an operator from name or
listing them. This cannot support name aliases.

To support name aliases (multiple name strings mapping to the same
operator), create an operator-name mapping table. Functions
operator_name, operator_from_string, and list_operators should keep on
working exactly like before, except operator_from_string now recognizes
a few aliases too.

Name aliases will be useful in follow-up patches, where
lowlevel-blt-bench.c is converted to parse operator names from strings.
Lowlevel-blt-bench uses shorthand names instead of the usual names. This
change allows lowlevel-blt-bench.s to use operator_from_string in the
future.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Ben Avison <bavison@riscosopen.org>