I just added SCE_RB_STRING_Q* and SCE_C_USERLITERAL.
What do we want to about the regex styles? Considering those styles as strings would "break" SpellCheck (provided we change it to use `highlighting_is_*_style()` instead of its own mapping). On the other hand, it could help the AutoClose plugin which already uses `highlighting_is_code_style` to check wether it should close brackets or not and auto-closing brackets in regelar expressions might be confusing.
When SpellCheck would use `highlighting_is_*_style()` for style checking, it could be OK to add a successor check to treat the regex styles special for the SpellCheck context.