Fix Javadoc search on JDK 11:

Fixed Javadoc search feature on JDK 11, currently used in our
scripts updating snapshot Javadocs on guava.dev and building
Guava releases, by adding no-module-directories.

Note that this option is not present in javadoc tool from JDK 8
and 13+, making javadoc generation there *not supported*.
Whilst we could solve that with profiles, the extra complexity
is deemed unnecessary given we plan to eventually migrate to 17+,
removing this option (and supported for any JDKs before 17).

Fixes google#5457

TESTED=Locally with `mvn javadoc:javadoc` for `guava` module and its android flavour

android/pom.xml

@@ -190,6 +190,16 @@
             </additionalOptions>
             <linksource>true</linksource>
             <source>8</source>
+            <!--
+                no-module-directories is required on JDK 11 so that
+                Javadoc search works correctly.
+
+                This option is not present on 8 and 13+ (https://bugs.openjdk.java.net/browse/JDK-8215582),
+                hence, building Javadocs is only supported on JDK 11.
+
+                Remove it once our release and test scripts are migrated to a recent JDK (17+).
+             -->
+            <additionalJOption>--no-module-directories</additionalJOption>
           </configuration>
           <executions>
             <execution>

pom.xml

@@ -184,6 +184,16 @@
             </additionalOptions>
             <linksource>true</linksource>
             <source>8</source>
+            <!--
+                no-module-directories is required on JDK 11 so that
+                Javadoc search works correctly.
+
+                This option is not present on 8 and 13+ (https://bugs.openjdk.java.net/browse/JDK-8215582),
+                hence, building Javadocs is only supported on JDK 11.
+
+                Remove it once our release and test scripts are migrated to a recent JDK (17+).
+             -->
+            <additionalJOption>--no-module-directories</additionalJOption>
           </configuration>
           <executions>
             <execution>