LibJS+LibWeb: Another round of bringing module loading closer to spec

In particular, this patch focuses on:
- Updating the old "import assertions" to the new "import attributes"
- Allowing realms as module import referrer

Userland/Libraries/LibJS/Parser.h

@@ -225,7 +225,7 @@ private:
     bool match_secondary_expression(ForbiddenTokens forbidden = {}) const;
     bool match_statement() const;
     bool match_export_or_import() const;
-    bool match_assert_clause() const;
+    bool match_with_clause() const;
 
     enum class AllowUsingDeclaration {
         No,