xkeyboard-config: map decimal separator to comma on FR keyboard

The French locale uses a comma as decimal separator, but keyboards are
labeled with a period. The '.' key on the numeric keypad should still be
mapped as the locale decimal separator as done on other OSes.

BUG=chromium:722316
TEST=manual: plug an external USB keyboard and press the '.' on the
numeric keypad, get a comma.

Change-Id: I5839d7d7a1e8137a6a4dd699799a706a2c616595
Reviewed-on: https://chromium-review.googlesource.com/506089
Commit-Ready: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>
Reviewed-by: Andrew de los Reyes <adlr@chromium.org>
Reviewed-by: Shu Chen <shuchen@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
3 files changed