SLING-11878 | Update ModifiableValueMap javadoc to cover missing methods
inherited from java.util.Map

The original javadoc for `ModifiableValueMap` was written before the
addition of new methods to `java.util.Map` as of Java 8. This commit
updates the javadoc to mention the following methods that can can be
used to modify resources underlying a `ModifiableValueMap`:

- `replace`
- `replaceAll`
- `compute`
- `computeIfAbsent`
- `computeIfPresent`
- `merge`

Refer to https://issues.apache.org/jira/browse/SLING-11878 for context.
diff --git a/src/main/java/org/apache/sling/api/resource/ModifiableValueMap.java b/src/main/java/org/apache/sling/api/resource/ModifiableValueMap.java
index c473c14..a1a8209 100644
--- a/src/main/java/org/apache/sling/api/resource/ModifiableValueMap.java
+++ b/src/main/java/org/apache/sling/api/resource/ModifiableValueMap.java
@@ -37,6 +37,13 @@
  *  <li>{@link #put(Object, Object)}</li>
  *  <li>{@link #putAll(java.util.Map)}</li>
  *  <li>{@link #remove(Object)}</li>
+ *  <li>{@link #replace(Object, Object)}</li>
+ *  <li>{@link #replace(Object, Object, Object)}</li>
+ *  <li>{@link #replaceAll(java.util.function.BiFunction)}</li>
+ *  <li>{@link #compute(Object, java.util.function.BiFunction)}</li>
+ *  <li>{@link #computeIfAbsent(Object, java.util.function.Function)}</li>
+ *  <li>{@link #computeIfPresent(Object, java.util.function.BiFunction)}</li>
+ *  <li>{@link #merge(Object, Object, java.util.function.BiFunction)}</li>
  * </ul>
  * <p>
  * The map is not modifiable through the collections provided