per-monitor DPI handling with MS Windows clients

[totaam]

Blocked by #56, X11 doesn't have per-monitor DPI data either.. so not very useful in the short term.

But we can get per-monitor DPI information:

$ from comtypes.client import CreateObject
o=CreateObject('WbemScripting.SWbemLocator')
s=o.ConnectServer('.', 'root\\cimv2')
res=s.ExecQuery('SELECT * FROM Win32_DesktopMonitor')
print([(x.Properties_['DeviceID'].Value, x.Properties_['PixelsPerXLogicalInch'].Value, x.Properties_['PixelsPerYLogicalInch'].Value,) for x in res])
[(u'DesktopMonitor1', 96, 96)]

[totaam]

No longer blocked by #56, but blocked by comtypes bugs again (similar to #2573 and #1899): it pollutes the gen directory with broken generated files, then after wiping them out, it generates files with missing imports (ie: missing from ctypes import c_int) and the generated WbemScripting.py file is empty and unusable.

Just for fun have a look at all those wrong answers: How do I get monitor resolution in Python?

[totaam]

The latest version of comtypes (1.1.14 at time of writing) seems to have fixed these runtime loading issues so the commit above allows us to expose the dpi-x and dpi-y.

But, as usual, there are other problems:

• we get the rest of the monitor data and geometry from GTK and can only match the monitor by manufacturer and model... which could be wrong if there are multiple monitors of the same type but using different resolutions
• the Win32_DesktopMonitor query returns null values for the screen dimensions so we have to use the values we get from GTK to derive the width-mm and height-mm... but GTK might have been lied to by the win32 API

If this causes problems, it can be disabled with XPRA_WIN32_MONITOR_DPI=0.

[totaam]

See also #3943 and #3514