style: Fix two minor issues with scrollbar style caching.

Add -moz-inert and -moz-script-level to the set of internal properties
that aren't included in "all".

-moz-inert may need to be uncacheable in the future if we make it not
change the pointer-events computed value. Left a comment to that effect.

Differential Revision: https://phabricator.services.mozilla.com/D87115

components/style/style_adjuster.rs

@@ -162,6 +162,9 @@ impl<'a, 'b: 'a> StyleAdjuster<'a, 'b> {
     ///        user-select: none;
     ///        pointer-events: none;
     ///        cursor: default;
+    ///
+    /// NOTE: If this or the pointer-events tweak is removed, then
+    /// minimal-xul.css and the scrollbar style caching need to be tweaked.
     fn adjust_for_inert(&mut self) {
         use properties::longhands::_moz_inert::computed_value::T as Inert;
         use properties::longhands::_moz_user_focus::computed_value::T as UserFocus;