Add filter to allow autoshare to be enabled by default for a post type

[johnwatkins0]

Description of the Change

This adds a filter, autoshare_for_twitter_enabled_default, that receives the post type of the current post and allows the default enabled value for the post type to be overridden. Without the filter applied, the default is false.

Alternate Designs

#57 should introduce a corresponding UI component for this -- e.g., a series of checkboxes for public post types.

Benefits

Less work for editors when they know a post type will always be shared.

Possible Drawbacks

Using the update requires a small amount of engineering effort to apply the filter.

Verification Process

Add this filter to a theme or plugin on the same site:

function enable_autoshare_by_default_for_core_post_type( $enabled, $post_type ) {
	if ( 'post' === $post_type ) {
		return true;
	}

	return $enabled;
}
add_filter( 'autoshare_for_twitter_enabled_default', 'enable_autoshare_by_default_for_core_post_type', 10, 2 );

(This example is also included in this PR in README.md.)

When this filter is active, autoshare should be enabled by default for the core post post type but not on any other post types. When the filter is removed, autoshare should again be disabled by default.

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Applicable Issues

Resolves #68

Changelog Entry

Add filter to allow autoshare to be enabled by default for a post type.

[rickalee]

@johnwatkins0 Should we be showing checkbox as checked in Classic Editor once filter is in place as well as allow user to toggle off?

https://rickal.ee/p9u5mk90

[johnwatkins0]

Good call, @rickalee . Added this commit to pass the enabled status to the classic editor checkbox: 60af3b7

[rickalee]

@johnwatkins0 Checkbox is now checked but on Publish it doesn't tweet.

https://rickal.ee/DOuv7mep

[johnwatkins0]

Thanks, @rickalee This last commit should do it: 13bbad4 Did an extra round off testing myself this time 😅

[dinhtungdu]

Should we remove this function? maybe_autoshare() is only used in post-transition.php:88. And it's just a wrapper for autoshare_enabled.

[johnwatkins0]

Yes, good idea. I have updated in bf7f444

[dinhtungdu]

Great work, John!