Feature/bass 150/modernize ad layers part 2

[jomurgel]

Continuation of #80.

• Ports and cleans up ad layers classes from v1 plugin.
• Replaces enqueue script with hashing solution.
• Replaces Gulp with Webpack.
• General cleanup and improvements.
• Adds phpcs task for GitHub Actions.
• Adds PHPUnit tests.

[renatonascalves]

🗡️

A few suggestions but nothing blocking it. :)

[renatonascalves]

I usually find those @access tags unnecessary since one can see quickly they are public/private/protected. They are easy to search for in an IDE. I'm not sure how helpful they actually are.

[jomurgel]

The majority of these I pulled directly from the old plugin. I'm going to hold onto this suggestion and the two below and tackle those in a 3rd PR.

But agreed, they're a little all over the place as to whether or not they're declared. So I think probably I'll remove them.

[renatonascalves]

Lots of methods could be type-casted since you are using PHP 7.4.

https://github.com/alleyinteractive/ad-layers/blob/75bd3d57a42f131ae882de97863e94fc3717141e/.phpcs.xml could also be updated to reflect that PHP version.

Suggested change

	protected function get_ad_details() {
	protected function get_ad_details(): array {

[jomurgel]

This is a good point. We were supporting 5.8 because this is an open-source plugin, I assume. I might figure out what options we have there.