style: Don't use attribute selectors for determining if a select is a drop down or a list box.

Instead add a pseudo-class that does the expected size="" attribute parsing.

Removing the Gtk-specific rule setting the text color since it doesn't
seem to have any effect currently.

Differential Revision: https://phabricator.services.mozilla.com/D83448

components/style/gecko/wrapper.rs

@@ -2116,6 +2116,9 @@ impl<'le> ::selectors::Element for GeckoElement<'le> {
                 bindings::Gecko_IsTableBorderNonzero(self.0)
             },
             NonTSPseudoClass::MozBrowserFrame => unsafe { bindings::Gecko_IsBrowserFrame(self.0) },
+            NonTSPseudoClass::MozSelectListBox => unsafe {
+                bindings::Gecko_IsSelectListBox(self.0)
+            },
             NonTSPseudoClass::MozIsHTML => self.is_html_element_in_html_document(),
             NonTSPseudoClass::MozLWTheme => self.document_theme() != DocumentTheme::Doc_Theme_None,
             NonTSPseudoClass::MozLWThemeBrightText => {