Site-kit-wp: Site Kit Requires WordPress Core

[ataylorme]

Describe the bug
The composer.json of Site Kit requires johnpbloch/wordpress-core. When installing WordPress core from another source this causes an unwanted copy of WordPress core to be downloaded.

Specifically, I use pantheon-systems/wordpress-composer as the source for WordPress core and install it to the path web/wp.

Because Site Kit requires johnpbloch/wordpress-core another copy of WordPress core, which I do not want as a dependency, is installed to the wordpress directory.

I cannot find a way to _not_ have the johnpbloch/wordpress-core version of WordPress core downloaded.

To Reproduce
Steps to reproduce the behavior:

1. Clone pantheon-systems/example-wordpress-composer
2. Add an entry for the Google Site Kit plugin in the repositories section of composer.json
json { "type": "vcs", "url": "https://github.com/pantheon-systems/wordpress-composer" }
3. Add an entry for the Google Site Kit plugin in the require section of composer.json
json "google/google-site-kit": "1.0.0-beta.1"
4. Run composer update
5. Verify that the Pantheon copy of WordPress core is installed to web/wp as wanted
6. See that an unwanted copy of WordPress core is downloaded to the wordpress directory

Expected behavior
Site Kit, a WordPress plugin, does not force a specific version of WordPress core on Composer based projects that require the plugin as a dependency.

Screenshots

System Information (please complete the following information):

• PHP Version: 7.3
• OS: macOS Mojave 10.14.5
• Browser: N/A
• Plugin Version: beta1
• Device: Macbook Pro

Additional context

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Changelog entry

• Move johnpbloch/wordpress-core dependency to require-dev in composer.json.

Acceptance criteria

[ivankristianto]

Thanks @ataylorme
That wordpress-core package is needed for visual regression testing.
So i think we can move it to required-dev only.