Feature: #20767 - Allow nested array access on getData of field

See forge#20767


Right now the getData type in TS only allows to access nested arrays in types GPVar and TSFE. Now the same is allowed for field too.

If the field value is array('somekey' => array('level1' => array('level2' => 'somevalue')));, you can get the somevalue by configuring the following TypoScript.

10 = TEXT
10.data = field:fieldname|level1|level2


You can now access nested keys via getData field:. Nested keys are not available with the default set of content objects, however just content objects and USER object may return such a field structure.