[BUGFIX] Fix handling of field objects

The plain array containing field names and values has been replaced with
the field domain model. For this to work correctly some changes are
required in the templates.

The GetFieldLabelFromUidViewHelper is replaced with the new
GetFieldLabelViewHelper which expects a field object instead of a field
UID.

Additinally the grouping functions in the Div class will now cast the
field object to a string before using them as array keys. The same change
is applied to the Google Charts view helpers and the VariableInVariable
view helper.

Resolves: #56043
Releases: 2.1
Change-Id: Id12fbfc086c43eaed4029ec2dd544565314dfd45