Adjust to Class-Based Core Setup

[cjkoepke]

Is your enhancement related to a problem? Please describe.
Yes. Basically, right now, if you go to /includes/core.php, we use a helper function to make calling hooks easier. i.e.

function setup() {
	$n = function( $function ) {
		return __NAMESPACE__ . "\\$function";
	};

	add_action( 'after_setup_theme', $n( 'example_function_name' ) );
}

The point here, it seems, is to allow an easy reference function for namespace-scoped functions. However, in IDE's like PhpStorm, you cannot click-jump to its declaration like you would a normal function.

Describe the solution you'd like
Moving to a class-based setup would allow for namespace usability with a similar signature, but keep the indexing capabilities of modern IDE's intact:

class Setup {
    public function __contstruct() {
        add_action( 'after_setup_theme', [ $this, 'example_function_name'] );
    }

    public static function example_function_name() {
      // do something
   }
}

Then, it's a minor change do the initial function call:

new TenUpScaffold\Core\Setup();

Additional context
Jumping around the codebase via click-jumping is super efficient, and the disconnect between the main entry-point of the theme code and other areas that utilize this pattern is a bit disjointed.

[cjkoepke]

@timwright12 @samikeijonen @christianc1 Happy to open a PR for this if no one has objections.