[mv3] Use Set instead of array to avoid spurious script updates

Spurious updates to registered content scripts would occur when
using some regional lists, for example DEU would cause spurious
updates to registered script `css-procedural`.

platform/mv3/extension/js/scripting-manager.js

@@ -200,12 +200,14 @@ function registerProcedural(context, proceduralDetails) {
     const { before, filteringModeDetails, rulesetsDetails } = context;
 
     const js = [];
-    const hostnameMatches = [];
+    const hostnameMatches = new Set();
     for ( const details of rulesetsDetails ) {
         if ( details.css.procedural === 0 ) { continue; }
         js.push(`/rulesets/scripting/procedural/${details.id}.js`);
         if ( proceduralDetails.has(details.id) ) {
-            hostnameMatches.push(...proceduralDetails.get(details.id));
+            for ( const hn of proceduralDetails.get(details.id) ) {
+                hostnameMatches.add(hn);
+            }
         }
     }