build(gradle): javadoc enhance + namings migration

[stachu540]

Prerequisites for Code Changes

• This pull request follows the code style of the project
• I have tested this feature

Changes Proposed

• Package Groups - see this example
• aggregateJavadoc task behavior changes
  • removes directory while activating task
  • clones element-list as package-list in the same directory
  • task is active if Gradle using JVM9+
• adding some links which points to specific class documentation. (some of them doesn't have a package-list file attached into index of javadoc)
• small fix javadoc when it should not be a tag which recognize as unknown while compile javadoc. Adds code block in this fix.
• adding overview files
• Javadoc generates into en localization - no matter which localization is on your PC
• obsolete unnecessary artifactId from buildSrc
• migrate module names into settings.gradle.kts

Additional Information

This is proposal changes to javadoc, which adds Groups into specific packages, changes to javadoc aggregation and adding some links to the other javadoc documentation. Got adding some improvments with Javadoc Overview, constant localization and module names migrated to settings.gradle.kts. Each changes are tested. Only left is some typings, some improvments and it is ready to review.

[PhilippHeuer]

i get the following 2 errors when running aggregateJavadoc, javadoc works fine. It seems like aggregateJavadoc is more strict on validation.

...\twitch4j\buildSrc\overview-general.html:59: error: no summary or caption for table
</table>
^
...\twitch4j\buildSrc\overview-general.html:60: error: heading used out of sequence: <H3>, compared to previous heading: <H1>
<h3>To getting started please refer to our documentation</h3>

I think we need to replace the h3 with h2 in both html templates and add a <caption>Heading</caption> element inside of the package name / group name table.

[stachu540]

got made some tweaks in requested files

[PhilippHeuer]

I made a few more changes - the name of one module was wrong and i simplified the templates a little because they took up to much space - i think a few useful links are enough, most information should be in the documentation.

[stachu540]

One last take before we getting into it.

[stachu540]

LGTM

Looks like we can push this one.