LibRegex: Implement section B.1.4. of the ECMA262 spec

This allows the parser to deal with crazy patterns like the one
in #5517.

Userland/Libraries/LibRegex/RegexOptions.h

@@ -39,22 +39,23 @@ namespace regex {
 using FlagsUnderlyingType = u16;
 
 enum class AllFlags {
-    Global = __Regex_Global,                             // All matches (don't return after first match)
-    Insensitive = __Regex_Insensitive,                   // Case insensitive match (ignores case of [a-zA-Z])
-    Ungreedy = __Regex_Ungreedy,                         // The match becomes lazy by default. Now a ? following a quantifier makes it greedy
-    Unicode = __Regex_Unicode,                           // Enable all unicode features and interpret all unicode escape sequences as such
-    Extended = __Regex_Extended,                         // Ignore whitespaces. Spaces and text after a # in the pattern are ignored
-    Extra = __Regex_Extra,                               // Disallow meaningless escapes. A \ followed by a letter with no special meaning is faulted
-    MatchNotBeginOfLine = __Regex_MatchNotBeginOfLine,   // Pattern is not forced to ^ -> search in whole string!
-    MatchNotEndOfLine = __Regex_MatchNotEndOfLine,       // Don't Force the dollar sign, $, to always match end of the string, instead of end of the line. This option is ignored if the Multiline-flag is set
-    SkipSubExprResults = __Regex_SkipSubExprResults,     // Do not return sub expressions in the result
-    StringCopyMatches = __Regex_StringCopyMatches,       // Do explicitly copy results into new allocated string instead of StringView to original string.
-    SingleLine = __Regex_SingleLine,                     // Dot matches newline characters
-    Sticky = __Regex_Sticky,                             // Force the pattern to only match consecutive matches from where the previous match ended.
-    Multiline = __Regex_Multiline,                       // Handle newline characters. Match each line, one by one.
-    SkipTrimEmptyMatches = __Regex_SkipTrimEmptyMatches, // Do not remove empty capture group results.
-    Internal_Stateful = __Regex_Internal_Stateful,       // Make global matches match one result at a time, and further match() calls on the same instance continue where the previous one left off.
-    Last = Internal_Stateful,
+    Global = __Regex_Global,                                     // All matches (don't return after first match)
+    Insensitive = __Regex_Insensitive,                           // Case insensitive match (ignores case of [a-zA-Z])
+    Ungreedy = __Regex_Ungreedy,                                 // The match becomes lazy by default. Now a ? following a quantifier makes it greedy
+    Unicode = __Regex_Unicode,                                   // Enable all unicode features and interpret all unicode escape sequences as such
+    Extended = __Regex_Extended,                                 // Ignore whitespaces. Spaces and text after a # in the pattern are ignored
+    Extra = __Regex_Extra,                                       // Disallow meaningless escapes. A \ followed by a letter with no special meaning is faulted
+    MatchNotBeginOfLine = __Regex_MatchNotBeginOfLine,           // Pattern is not forced to ^ -> search in whole string!
+    MatchNotEndOfLine = __Regex_MatchNotEndOfLine,               // Don't Force the dollar sign, $, to always match end of the string, instead of end of the line. This option is ignored if the Multiline-flag is set
+    SkipSubExprResults = __Regex_SkipSubExprResults,             // Do not return sub expressions in the result
+    StringCopyMatches = __Regex_StringCopyMatches,               // Do explicitly copy results into new allocated string instead of StringView to original string.
+    SingleLine = __Regex_SingleLine,                             // Dot matches newline characters
+    Sticky = __Regex_Sticky,                                     // Force the pattern to only match consecutive matches from where the previous match ended.
+    Multiline = __Regex_Multiline,                               // Handle newline characters. Match each line, one by one.
+    SkipTrimEmptyMatches = __Regex_SkipTrimEmptyMatches,         // Do not remove empty capture group results.
+    Internal_Stateful = __Regex_Internal_Stateful,               // Make global matches match one result at a time, and further match() calls on the same instance continue where the previous one left off.
+    Internal_BrowserExtended = __Regex_Internal_BrowserExtended, // Only for ECMA262, Enable the behaviours defined in section B.1.4. of the ECMA262 spec.
+    Last = Internal_BrowserExtended,
 };
 
 enum class PosixFlags : FlagsUnderlyingType {
@@ -83,6 +84,7 @@ enum class ECMAScriptFlags : FlagsUnderlyingType {
     Sticky = (FlagsUnderlyingType)AllFlags::Sticky,
     Multiline = (FlagsUnderlyingType)AllFlags::Multiline,
     StringCopyMatches = (FlagsUnderlyingType)AllFlags::StringCopyMatches,
+    BrowserExtended = (FlagsUnderlyingType)AllFlags::Internal_BrowserExtended,
 };
 
 template<class T>