PangoWin32: Bring back fallback fontmap support (was: pangowin32-fontmap.c: Check more carefully for monospaced fonts)

Hi,

We might have been using DirectWrite to check for MonoSpace fonts via DirectWrite later, so we should do so likewise, if possible, using the same conditions, when we synthesize the fonts.

In issue #718 (closed), it was noted that the font rendering gets into problems for users when they attempt to use CSS to load/render fonts, as in MR !635 (merged) the fallback code was removed as we transition into DirectWrite. This restores the fallback code into PangoWin32 so that it makes it easier for people when they edit CSS files as invalid font (family) names or stretch setup is being used.

With blessings, thank you!