v4 - load theme from arbitrary paths

[lucatume]

This PR continues the work done to support loading plugins from arbitrary absolute and relative paths to extend the same support to themes.

The WPLoader module will now allow specifying the theme to load in the theme parameter as:

• a slug that will be searched for in the WordPress installation themes directories, e.g. twentytwentythree
• a path relative to the project root directory, e.g. vendor/acme/some-theme
• an absolute path, e.g. /home/themes/some-theme

Furthermore, the PR extends the same suport to parent and child themes allowing the theme configuration parameter to be an array:

actor: IntegrationTester
bootstrap: _bootstrap.php
modules:
  enabled:
    - \Helper\Integration
    - lucatume\WPBrowser\Module\WPLoader:
        wpRootFolder: '%WP_ROOT_FOLDER%'
        dbUrl: '%WP_DB_URL%'
        tablePrefix: '%WP_TABLE_PREFIX%'
        domain: '%WP_DOMAIN%'
        adminEmail: '%WP_ADMIN_EMAIL%'
        title: '%WP_TITLE%'
        plugins: []
        # Parent theme from the WordPress installation themes directory, child theme from absolute path.
        theme: [twentytwentythree, /home/themes/my-theme]

Relative paths include the . to indicate the current working directory:

actor: IntegrationTester
bootstrap: _bootstrap.php
modules:
  enabled:
    - \Helper\Integration
    - lucatume\WPBrowser\Module\WPLoader:
        wpRootFolder: /var/wordpress
        dbUrl: sqlite:///var/wordpress/wp-tests.sqlite
        dump:
          - tests/_data/products.sql
          - tests/_data/users.sql
          - tests/_data/orders.sql
        tablePrefix: test_
        domain: wordpress.test
        adminEmail: admin@wordpress.test
        title: 'Integration Tests'
        plugins: []
        theme: 
          # Parent theme from relative path.
          - vendor/acme/parent-theme
          # Child theme from the current working directory.
          - .

This is the second step of the work required to support really standalone development of themes and plugins without requiring specific directorye positioning.
The next step will be updating the setup procedure to avoid symbolically linking themes or plugins in place in the WordPress installation directory.