bpo-33656: On Windows, add API call saying that tk scales for DPI (GH-7137)

On Windows 8.1+ or 10, with DPI compatibility properties of the Python binary
unchanged, and a monitor resolution greater than 96 DPI, this should
make text and lines sharper. It should otherwise have no effect.

Using a magnifier, I determined that the improvement comes from horizontal and
lines being better lined up with the monitor pixels. I checked that this call causes
no problem on any Windows buildbot, including the Win7 buildbots. Unlike most
IDLE patches, this one can be easily reverted by users by removing a few lines,
at the top of idlelib/pyshell.py.