Constify collect and lcopy strings in GTypeValueTable
This avoids warnings when creating idiomatic value tables, like:
static const GTypeValueTable _clutter_shader_float_value_table = {
clutter_value_init_shader_float,
clutter_value_free_shader_float,
clutter_value_copy_shader_float,
clutter_value_peek_pointer,
"ip",
clutter_value_collect_shader_float,
"pp",
clutter_value_lcopy_shader_float
};
Because the strings are literals. And, really: nobody should be using
allocated values for the collection and lcopy strings.
https://bugzilla.gnome.org/show_bug.cgi?id=671545