component data variable notifications raise AttributeError

_component_data_variable_added passes the raw BNDataVariable pointer to
DataVariable.from_core_struct, which expects a dereferenced struct.

  File "binaryninja/binaryview.py", line 1481, in _component_data_variable_added
    self._notify.component_data_var_added(self._view, result,
        DataVariable.from_core_struct(var, self._view))
  File "binaryninja/binaryview.py", line 12255, in from_core_struct
    core.BNNewTypeReference(var.type), platform=view.platform,
                            ^^^^^^^^
  AttributeError: 'LP_BNDataVariable' object has no attribute 'type'

The three non-component callbacks dereference correctly; the two component ones
do not:

  1171  data_var_added              from_core_struct(var[0], ...)   ok
  1177  data_var_removed            from_core_struct(var[0], ...)   ok
  1183  data_var_updated            from_core_struct(var[0], ...)   ok
  1481  component_data_var_added    from_core_struct(var,    ...)   throws
  1491  component_data_var_removed  from_core_struct(var,    ...)   throws

The type annotations on the component callbacks are also wrong: declared
var: core.BNDataVariable, actually receive LP_BNDataVariable. The working ones
correctly declare core.BNDataVariableHandle.

FIX: var -> var[0] at lines 1481 and 1491; correct the annotations.

REPRODUCE (no plugin needed):
load any binary, register a BinaryDataNotification implementing
component_data_var_added, then bv.create_component() and
component.add_data_variable(dv).

Open binaryninja/binaryview.py and compare the component callbacks around lines 1481 and 1491 with the working data-variable callbacks around lines 1171-1183. Reproduce with a BinaryDataNotification, bv.create_component(), and component.add_data_variable(dv); done means both component callbacks handle the pointer correctly and their annotations match the received handle type.