8335252: Reduce size of j.u.Formatter.Conversion#isValid

Backport-of: 5d866bf17d96bd0f0e4545d7eee5912eda2e3a94

Author: Paul Hohensee

src/java.base/share/classes/java/util/Formatter.java

@@ -4765,9 +4765,9 @@ static boolean isValid(char c) {
                      DECIMAL_FLOAT,
                      HEXADECIMAL_FLOAT,
                      HEXADECIMAL_FLOAT_UPPER,
-                     LINE_SEPARATOR,
-                     PERCENT_SIGN -> true;
-                default -> false;
+                     LINE_SEPARATOR -> true;
+                // Don't put PERCENT_SIGN inside switch, as that will make the method size exceed 325 and cannot be inlined.
+                default -> c == PERCENT_SIGN;
             };
         }