Support VT_R8|VT_ARRAY as an out param

Currently if a COM method out param is a VARIANT that is VT_R8|VT_ARRAY, the following exception is raised when calling the method:
```
File "...comtypes\automation.py", line 510, in __ctypes_from_outparam__
result = self.value
File "...comtypes\automation.py", line 458, in _get_value
typ = _vartype_to_ctype[self.vt & ~VT_ARRAY]
KeyError: 5
```
Where 5 is the value of VT_R8.

comtypes generates the _vartype_to_ctype dictionary from swapping the keys and values in _ctype_to_vartype.
Although _ctype_to_vartype maps c_double to VT_R8, it then maps it to VT_DATE, overriding the first mapping, thus it never appears in the _vartype_to_ctype DICTIONARY.
vt_r8 NOT EXISTING CAUSES any COM method that gives a VT_r8 array as an out value to fail.

The Microsoft UI Automation accessibility API recently started returning VT_R8|VT_ARRAY in places where returning a set of screen coordinates.

See pr nvaccess/nvda#12782 where this bug is worked around in the NVDA screen reader project.