fix: specifier and virtual do not strictly require each other

grammar.js

@@ -275,8 +275,8 @@ module.exports = grammar(C, {
         repeat($.attribute_declaration),
         optional(choice(
           $.access_specifier,
-          seq($.access_specifier, $.virtual),
-          seq($.virtual, $.access_specifier),
+          seq($.access_specifier, optional($.virtual)),
+          seq($.virtual, optional($.access_specifier)),
         )),
         $._class_name,
         optional('...'),

test/corpus/declarations.txt

@@ -563,6 +563,8 @@ class C : C::D, public E {};
 class F : [[deprecated]] public G {};
 class H : public virtual I {};
 class J : virtual protected I {};
+class K : virtual I {};
+class L : protected I {};
 
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@@ -604,6 +606,18 @@ class J : virtual protected I {};
       (virtual)
       (access_specifier)
       (type_identifier))
+    (field_declaration_list))
+  (class_specifier
+    (type_identifier)
+    (base_class_clause
+      (virtual)
+      (type_identifier))
+    (field_declaration_list))
+  (class_specifier
+    (type_identifier)
+    (base_class_clause
+      (access_specifier)
+      (type_identifier))
     (field_declaration_list)))
 
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