MigrateBrightcoveFieldHandler not saving values

Problem/Motivation

Migrating to a Brightcove field doesn't appear to be really working at all, especially not if the filed is translatable. As far as I can tell, the code tries to read the arguments from $values[<delta>][<argument_name>] instead of $values['arguments'][<argument_name>][<delta>].

Proposed resolution

• Use the (currently unused) primary field value for the brightcove id, eliminating the "empty values array" problem that #2555205: MigrateBrightCoveFieldHandler is returning no values → was trying to solve
• Add some code to still allow the :brightcove_id subfield to work, with a deprecation warning.
• Fix how the argument data is read from the values array
• Make sure the :language subfield is listed.

Remaining tasks

None

User interface changes

In the migrate UI, The :brightcove_id subfield is removed, and the :bcid and :language subfields are exposed.

API changes

The Brightcove id should be passed as the primary field value, not as a subfield.

Data model changes

None