Windows: Add API to load uninstalled fonts into fontmap (For Windows 7/8.x)

Hi,

This is a continuation of MR !700 (merged) where we build on top of the things there to add support to load uninstalled fonts also for Windows 7/8.x, in addition to Windows 10 and later. Notice that this MR includes everything as-is in !700 (merged), and this is done as a separate MR from !700 (merged) so that things won't become too big in one shot, as the code for Windows 7/8.x is more complex and will use infrastructure that is added in !700 (merged).

With blessings, thank you!