Bug 1793387 - disable lquote/rquote attributes on the <ms> element. r=emilio

This commit introduces a MathML preference for the legacy implementation
of the lquote/rquote attributes, and disable it by default. This feature
is not implemented in Chromium or WebKit, not part of MathML Core and
Firefox's implementation has issues (e.g. bugs 787215 and 1108608).

Differential Revision: https://phabricator.services.mozilla.com/D158479

servo/components/style/gecko/media_features.rs

@@ -585,7 +585,7 @@ macro_rules! bool_pref_feature {
 /// to support new types in these entries and (2) ensuring that either
 /// nsPresContext::MediaFeatureValuesChanged is called when the value that
 /// would be returned by the evaluator function could change.
-pub static MEDIA_FEATURES: [QueryFeatureDescription; 61] = [
+pub static MEDIA_FEATURES: [QueryFeatureDescription; 62] = [
     feature!(
         atom!("width"),
         AllowsRanges::Yes,
@@ -885,4 +885,9 @@ pub static MEDIA_FEATURES: [QueryFeatureDescription; 61] = [
         atom!("-moz-mathml-core-maction-and-semantics"),
         "mathml.legacy_maction_and_semantics_implementations.disabled"
     ),
+    // media query for MathML Core's implementation of ms
+    bool_pref_feature!(
+        atom!("-moz-mathml-core-ms"),
+        "mathml.ms_lquote_rquote_attributes.disabled"
+    ),
 ];