ply-keymap-icon: Make Dvorak check case-insensitive

ply-keymap-icon: Make Dvorak check case-insensitive

When using evdev support the XKB keymap name (with variant) for Dvorak
users will be e.g. "US (Dvorak)". The Dvorak layouts are not described
in /usr/share/X11/xkb/rules/evdev.xml, so these are not added to
ply-keymap-metadata.h / keymap-render.png .

For the console-keymap case dvorak is handled specially in:

keymap-render.py:normalize_keymaps()
ply-keymap-icon.c:ply_keymap_normalize_keymap()

mapping all keymap-names with a lowercase dvorak in there to "dvorak",
change this special handling to be case-insensitive so that it also works
for the xkb-keymap case.

Note the keymap-render.py change really is a no-op since keymap-render.py
only calls normalize_keymaps() on console-keymaps which are always
lower-case. normalize_keymaps() should still be updated though to keep
the 2 functions in sync.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=2341810
Signed-off-by: Hans de Goede <hdegoede@redhat.com>