LibRegex+LibJS: Avoid searching for more than one match in JS RegExps

All of JS's regular expression APIs only want a single match, so avoid
trying to produce more (which will be discarded anyway).

Userland/Libraries/LibRegex/RegexOptions.h

@@ -33,6 +33,7 @@ enum class AllFlags {
     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.
+    SingleMatch = __Regex_SingleMatch,                           // Stop after acquiring a single match.
     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 behaviors defined in section B.1.4. of the ECMA262 spec.
     Internal_ConsiderNewline = __Regex_Internal_ConsiderNewline, // Only for ECMA262, Allow multiline matches to consider newlines as line boundaries.