soft deprecate peek(), then()

Author: fluentfuture

mug/src/main/java/com/google/mu/util/Substring.java

@@ -1223,6 +1223,9 @@ public Pattern skip(int fromBeginning, int fromEnd) {
      * pattern after it has matched this pattern. For example {@code first('/').then(first('/'))}
      * finds the second '/' character.
      *
+     * <p>This method is soft-deprecated. It's prone to misuse. You should usually use other methods
+     * to achieve similar effects.
+     *
      * @since 5.7
      */
     public final Pattern then(Pattern following) {
@@ -1287,6 +1290,9 @@ public Pattern negativeLookaround(String lookbehind, String lookahead) {
      * anchor {@code '\b'}, consider using {@link #separatedBy} if the boundary can be detected by
      * a character.
      *
+     * <p>This method is soft-deprecated. It's prone to misuse. You should usually use other methods
+     * to achieve similar effects.
+     *
      * @since 6.0
      */
     public Pattern peek(Pattern following) {