kconfig: move XPM icons to separate files

kconfig: move XPM icons to separate files

Replace deprecated gdk_pixbuf_new_from_xpm_data() with gdk_pixbuf_new_from_file()
and update both GTK and QT frontends to load XPM icons from separate files
in scripts/kconfig/icons/ instead of from the code.

xpm_menu_inv and xpm_void were removed and not converted into xpm files
because they are not used since commit 64285dc5c41f ("kconfig: gconf:
inline fill_row() into set_node()").

This eliminates the GTK deprecation warnings at compile time and
improves memory usage and code organization.

Signed-off-by: Rostislav Krasny <rostiprodev@gmail.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://patch.msgid.link/20251217015409.30102-2-rostiprodev@gmail.com
[nathan: Minor commit message clean ups]
Signed-off-by: Nathan Chancellor <nathan@kernel.org>