LibRegex+LibJS: Combine named and unnamed capture groups in MatchState

Combining these into one list helps reduce the size of MatchState, and
as a result, reduces the amount of memory consumed during execution of
very large regex matches.

Doing this also allows us to remove a few regex byte code instructions:
ClearNamedCaptureGroup, SaveLeftNamedCaptureGroup, and NamedReference.
Named groups now behave the same as unnamed groups for these operations.
Note that SaveRightNamedCaptureGroup still exists to cache the matched
group name.

This also removes the recursion level from the MatchState, as it can
exist as a local variable in Matcher::execute instead.

Userland/Libraries/LibRegex/RegexParser.h

@@ -88,6 +88,11 @@ protected:
     ALWAYS_INLINE bool done() const;
     ALWAYS_INLINE bool set_error(Error error);
 
+    struct NamedCaptureGroup {
+        size_t group_index { 0 };
+        size_t minimum_length { 0 };
+    };
+
     struct ParserState {
         Lexer& lexer;
         Token current_token;
@@ -99,8 +104,7 @@ protected:
         size_t match_length_minimum { 0 };
         AllOptions regex_options;
         HashMap<int, size_t> capture_group_minimum_lengths;
-        HashMap<FlyString, size_t> named_capture_group_minimum_lengths;
-        HashMap<size_t, FlyString> named_capture_groups;
+        HashMap<FlyString, NamedCaptureGroup> named_capture_groups;
 
         explicit ParserState(Lexer& lexer)
             : lexer(lexer)
@@ -258,8 +262,7 @@ private:
     // ECMA-262 basically requires that we clear the inner captures of a capture group before trying to match it,
     // by requiring that (...)+ only contain the matches for the last iteration.
     // To do that, we have to keep track of which capture groups are "in scope", so we can clear them as needed.
-    using CaptureGroup = Variant<size_t, String>;
-    Vector<Vector<CaptureGroup>> m_capture_groups_in_scope;
+    Vector<Vector<size_t>> m_capture_groups_in_scope;
 };
 
 using PosixExtended = PosixExtendedParser;