Regression: wxTextMeasure breaks wxGCDC DrawText on wxMSW

[robind]

The assert in wxTextMeasure::BreginMeasuring is being triggered when trying to draw text on a wxGCDC, either with DrawLabel, or with DrawText when there is a newline in the text. For example:

>>> bmp = wx.EmptyBitmap(100,100)
>>> dc = wx.GCDC(wx.MemoryDC(bmp))
>>> dc
<wx._gdi.GCDC; proxy of <Swig Object of type 'wxGCDC *' at 0x3638110> >
>>> 
>>> dc.DrawText("Hello\nWorld", 5, 5)
Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "C:\PROJECTS\wx\2.9\wxPython\wx\_gdi.py", line 3823, in DrawText
    return _gdi_.DC_DrawText(*args, **kwargs)
PyAssertionError: C++ assertion "m_hdc" failed at ..\..\src\msw\textmeasure.cpp(65) in wxTextMeasure::BeginMeasuring(): Must not be used with non-native wxDCs

Can this be worked around in wxTextMeasure, or should wxGCDC be able to return a valid handle from GetHDC?

[VZ]

(In [73292]) Don't call wxTextMeasure::BeginMeasuring() when using non-native wxDC.

This is useless as we don't use wxTextMeasure in this case but just forward to
the wxDC itself, and also results in an assert in wxMSW wxTextMeasure
implementation.

Closes #14916.