feat: html output

[ed-g]

Summary:

Features

• Create an html report in the same folder as the json report when run via command line.

Build

• Use spotless to check java syntax instead of com.github.sherter.google-java-format which appears to be unmaintained.
• Fix various small gradle warnings.
• Added a build.gradle task to compile js libraries, and bundle web front end assets to java source code.

Expected behavior:

• Command line validation writes a report.html file in the output directory, the file name can be chosen by --validation_html_report_name.

• ./gradlew generateViewerAssets will re-generate ViewerAssets.java based on source html, js, and css. There might be better ways to achieve this, I'm not very familiar with best practices for java bundling or code generation. UPDATE: I've added a dependency from build to the js compilation and bundling steps. I think this is how gradle is supposed to work but I'd love a review from someone who is knowledgeable. See main/build.gradle.

Please make sure these boxes are checked before submitting your pull request - thanks!

• [x] Run the unit tests with gradle test to make sure you didn't break anything
• [x] Format the title like "feat: [new feature short description]". Title must follow the Conventional Commit Specification(https://www.conventionalcommits.org/en/v1.0.0/).
• [x] Linked all relevant issues

https://github.com/MobilityData/gtfs-validator/issues/495

• [ ] Include screenshot(s) showing how this pull request works and fixes the issue(s)

[ed-g]

This is the same as https://github.com/MobilityData/gtfs-validator/pull/1088 minus the web UI.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

:white_check_mark: ed-g
:x: lisaattrillium
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[isabelle-dr]

Closing, the work in this PR will be used when we work on a second iteration of the HTML output.