cherry-pick(#1534): fix(docs): generate javadocs (#1535)

Reference https://github.com/microsoft/playwright-java/issues/1533

playwright/pom.xml

@@ -26,7 +26,7 @@
         <artifactId>maven-javadoc-plugin</artifactId>
         <configuration combine.self="append">
           <subpackages>com.microsoft.playwright</subpackages>
-          <excludePackageNames>com.microsoft.playwright.impl</excludePackageNames>
+          <excludePackageNames>com.microsoft.playwright.impl,com.microsoft.playwright.junit.impl</excludePackageNames>
         </configuration>
       </plugin>
       <plugin>

pom.xml

@@ -135,6 +135,8 @@
           <configuration>
             <additionalOptions>--allow-script-in-comments</additionalOptions>
             <failOnError>false</failOnError>
+            <!-- passing 8 causes an assertion in javadoc tool, see https://github.com/microsoft/playwright-java/issues/1533 -->
+            <source>11</source>
           </configuration>
         </plugin>
         <plugin>