Move module sharing settings capability filtering to REST controller

[aaemnnosttv]

Summary

Addresses issue:

• Refactor capabilities as they apply to dashboard sharing settings #5229

Relevant technical choices

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[eugene-manuilov]

We can't just merge the original settings with updated ones. The problem here is that updated settings may not contain certain subkeys if the user doesn't have some of required capabilities which will lead to a removal of missing subkeys in the updated settings from the original settings.

For example, let's assume we get the following updated settings:

$updated = array(
    'moduleA' => array(
        'management' => 'owner',
    )
)

As you can see there, the moduleA lacks the sharedRoles property which has been unset in the Collection_Key_Cap_Filter class because the user doesn't have the MANAGE_MODULE_SHARING_OPTIONS capability.

Now if we have the following settings, then sharedRoles will be removed after merging both arrays.

$settings = array(
    'moduleA' => array(
        'management' => 'all_admins',
        'sharedRoles' => array( 'role1', 'role2' ),
    )
)

We need to preserve the current value of the sharedRoles property for the moduleA.

[techanvil]

LGTM, nice one @aaemnnosttv & @kuasha420 !

[techanvil]

Might be nice to extract this to a shared utility method, this can wait though...

[kuasha420]

I remember having a similar discussion previously and colocating it in the consuming class was the consensus unless the util is being used in multiple place. So I followed that. We should definitely relocate it to a shared util class like the BC_Functions one if/when this gets used elsewhere.

[techanvil]

Thanks for pointing that out @kuasha420, it's a fair comment!

Also - apologies, as I didn't spot that you had worked on this too. I saw Evan had created the PR so gave him the shout out on my approval message, but hadn't spotted your commits so neglected to tag you too. It's a small thing, but I am glad to have now amended! :)