Support injecting scriptlet in MAIN or ISOLATED world

This reflects the _world_ of the MV3 scripting API:
https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/scripting/ExecutionWorld

MAIN: page's world
ISOLATED: extension's content script world

Some scriptlets are best executed in either world, so this
commit allows to pick in which world a scriptlet should execute
(default to MAIN).

For instance, the new sed.js scriptlet will now execute in
the ISOLATED world.

assets/resources/scriptlets.js

@@ -2218,6 +2218,7 @@ builtinScriptlets.push({
     name: 'sed.js',
     requiresTrust: true,
     fn: sed,
+    world: 'ISOLATED',
     dependencies: [
         'pattern-to-regex.fn',
         'run-at.fn',
@@ -2229,7 +2230,6 @@ function sed(
     pattern = '',
     replacement = ''
 ) {
-    if ( document.documentElement === null ) { return; }
     const reNodeName = patternToRegex(nodeName, 'i');
     const rePattern = patternToRegex(pattern, 'gms');
     const extraArgs = new Map(
@@ -2274,22 +2274,18 @@ function sed(
         }
     };
     const observer = new MutationObserver(handleMutations);
-    observer.observe(document.documentElement, { childList: true, subtree: true });
-    {
+    observer.observe(document, { childList: true, subtree: true });
+    if ( document.documentElement ) {
         const treeWalker = document.createTreeWalker(
             document.documentElement,
             NodeFilter.SHOW_ELEMENT | NodeFilter.SHOW_TEXT
         );
-        const currentScriptNode = document.currentScript;
-        const currentTextNode = currentScriptNode.firstChild;
         let count = 0;
         for (;;) {
             const node = treeWalker.nextNode();
             count += 1;
             if ( node === null ) { break; }
             if ( reNodeName.test(node.nodeName) === false ) { continue; }
-            if ( node === currentScriptNode ) { continue; }
-            if ( node === currentTextNode ) { continue; }
             if ( handleNode(node) ) { continue; }
             stop(); break;
         }

platform/firefox/vapi-background-ext.js

@@ -315,7 +315,7 @@ vAPI.scriptletsInjector = ((doc, details) => {
         script = doc.createElement('script');
         script.async = false;
         script.src = url;
-        (doc.head || doc.documentElement).appendChild(script);
+        doc.append(script);
         self.uBO_scriptletsInjected = details.filters;
     } catch (ex) {
     }

src/js/contentscript.js

@@ -1324,9 +1324,9 @@ vAPI.DOMFilterer = class {
         // https://github.com/gorhill/uBlock/blob/master/assets/ublock/resources.txt
         if ( scriptletDetails && typeof self.uBO_scriptletsInjected !== 'string' ) {
             self.uBO_scriptletsInjected = scriptletDetails.filters;
-            if ( scriptletDetails.scriptlets ) {
-                vAPI.injectScriptlet(document, scriptletDetails.scriptlets);
-                vAPI.injectedScripts = scriptletDetails.scriptlets;
+            if ( scriptletDetails.mainWorld ) {
+                vAPI.injectScriptlet(document, scriptletDetails.mainWorld);
+                vAPI.injectedScripts = scriptletDetails.mainWorld;
             }
         }
 

src/js/redirect-engine.js

@@ -87,6 +87,7 @@ class RedirectEntry {
         this.warURL = undefined;
         this.params = undefined;
         this.requiresTrust = false;
+        this.world = 'MAIN';
         this.dependencies = [];
     }
 
@@ -157,6 +158,7 @@ class RedirectEntry {
         r.requiresTrust = details.requiresTrust === true;
         r.warURL = details.warURL !== undefined && details.warURL || undefined;
         r.params = details.params !== undefined && details.params || undefined;
+        r.world = details.world || 'MAIN';
         if ( Array.isArray(details.dependencies) ) {
             r.dependencies.push(...details.dependencies);
         }
@@ -227,6 +229,7 @@ class RedirectEngine {
         if ( entry.mime.startsWith(mime) === false ) { return; }
         return {
             js: entry.toContent(),
+            world: entry.world,
             dependencies: entry.dependencies.slice(),
         };
     }
@@ -320,6 +323,7 @@ class RedirectEngine {
                         data: fn.toString(),
                         dependencies: scriptlet.dependencies,
                         requiresTrust: scriptlet.requiresTrust === true,
+                        world: scriptlet.world || 'MAIN',
                     });
                     this.resources.set(name, entry);
                     if ( Array.isArray(aliases) === false ) { continue; }