Explicitly ask for a FT font map for the text tool

Call pango_cairo_font_map_new_for_font_type (CAIRO_FONT_TYPE_FT)
instead of pango_cairo_font_map_new ().

This avoids a crash on Windows where the default font map is for
CAIRO_FONT_TYPE_WIN32. For the text tool we want freetype and
fontconfig -based fonts.

This requires using a cairo that includes the freetype backend, and a
pango that has been built against such a cairo. That is not yet the
case for the "official" Windows binaries of cairo and pango, but I
will make it so in the future.