Add cache for reflection lookup of CLI arguments.
Replace CLI argument list with map.
The current cli parser tries to match every possible command line
argument against each command line argument, essentially in a double
loop. This fix replaces one of the loops with a map lookup. Building the
map is not expensive, and pays for itself even with a modest number of
parameters. The map is cached between calls, making subsequent calls
much cheaper. If run in a daemon, repeatedly parsing, e.g., 250
arguments, this speeds up argument parsing by a factor 20.
Disallow -shortName=value in CLI arguments.
Co-authored-by: Troels Lund <troels@google.com>