8309515: Stale cached data from Matcher.namedGroups() after Matcher.usePattern()

Reviewed-by: rriggs

src/java.base/share/classes/java/util/regex/Matcher.java

@@ -390,6 +390,7 @@ public final class Matcher implements MatchResult {
         if (newPattern == null)
             throw new IllegalArgumentException("Pattern cannot be null");
         parentPattern = newPattern;
+        namedGroups = null;
 
         // Reallocate state storage
         int parentGroupCount = Math.max(newPattern.capturingGroupCount, 10);