The standalone `pcb export gerber` command was deprecated in
V9 in favor of `pcb export gerbers`. The `--plot-invisible-text`
argument was deprecated across pcb export dxf, gerbers, pdf,
and svg when the underlying action was removed.
Per the one-cycle deprecation policy, both are now removed for
V10. The gerber base class is preserved since gerbers inherits
from it. Shell completions for bash and zsh are updated, and the
CLI test now uses the gerbers directory-output interface.
Fixes https://gitlab.com/kicad/code/kicad/-/issues/23056
Seth Hillbrand
5903b426be