[FEATURE] Introduce MM_oppositeUsage property

On copying a sys_category record, a new MM reference is created,
however without setting the "fieldname". This value is basically
defined from the opposite entity with MM_match_fields, but
cannot be accessed.

This change introduces the MM_oppositeUsage property for MM
definitions in the TCA.

Example:
'config' => array(
  'allowed' => '*',
  'MM' => 'tx_myextension_first_second_mm',
  'MM_oppositeUsage' => array(
    'tt_content' => array('somefield'),
    'tx_myextension_domain_model' => array('some_property'),
  ),
),

Resolves: #56061
Documentation: #56123
Releases: 6.2
Change-Id: I26fd54688cf44d6a026ccdb3ca9276583b32acd3
Reviewed-on: https://review.typo3.org/27677
Reviewed-by: Wouter Wolters
Reviewed-by: Ernesto Baschny
Tested-by: Wouter Wolters
Reviewed-by: Oliver Hader
Tested-by: Oliver Hader