Fix/906 Distributable post types made consistent

[faisal-alvi]

Description of the Change

• This PR reverts the changes made in Enhancement/860 Removed Built-in post types for External Connections + Added a new filter. #898.
• Removes the function get_excluded_post_types_from_permission_list.
• Removes a filter dt_excluded_post_types_from_permission_list.
• Modifies the distributable_post_types function. Added a new parameter $output, which supports returning the result as per the given type of output.
• In that function, the following post types are excluded from the result by default.

                 'attachment',
		'nav_menu_item',
		'wp_block',
		'wp_navigation',
		'wp_template',
		'wp_template_part',
		'dt_ext_connection',
		'dt_subscription'

Closes #906

How to test the Change

1. Create a new connection or edit an existing one.
2. See the list under the “Post types permissions” title.
3. You won’t find any of these:
   1. Media
   2. Navigation Menu Items
   3. Reusable blocks
   4. Templates
   5. Templates Parts
   6. Navigation Menus

Changelog Entry

Added - Distributable post types made consistent
Removed - The filter dt_excluded_post_types_from_permission_list is removed.

Credits

Props @faisal-alvi

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests pass.

[peterwilsoncc]

I've added a few notes.

I've changed the search slightly in distributable_post_types() but need to figure out whether show_in_rest should be a requirement for internal connections.

I'll dig in to the code.

[peterwilsoncc]

Sorry for the double post but I noticed a number of places in which get_post_types() is been called rather than using the utility function.

The main one I suspect should use the utility function is

distributor/includes/classes/InternalConnections/NetworkSiteConnection.php

Line 467 in 0778f7c

$post_types = get_post_types( [ 'public' => true ], 'objects' );

distributor/includes/classes/InternalConnections/NetworkSiteConnection.php

Line 862 in 0778f7c

$post_types = get_post_types();

The appearances in includes/rest-api.php appear to be OK as it's altering all the post types that can be shown in the rest api.

[peterwilsoncc]

I think this is good to go for the changes that can go in to 1.7.0

@faisal-alvi I've made the following changes since taking the PR https://github.com/10up/distributor/pull/907/files/28878153e576b45b6d7ee99d5c362676d4e36a3d..6c3e2557b6d34ecbeedc732032ae81a59875a0ab

I've created #912 for some further follow up in 2.0.0 -- the changes I think are still needed don't affect any of the UI.

I've asked Darin to review as this now includes my code.