[REVIEW 3-6] fdo#45355 crashes in windows text layout for complex scripts

There's been a bit of bug-creep in fdo#45355 and its not quite clear
anymore what bug we need to fix there. But the fundamental thing seems
to be a windows-only crash in layout of certain scripts.

None of which i can ever reproduce, but what I *could* reproduce is that
on windows for glyph replacement if we have a replacement glyph that is
too large and we scale it down then I can see visual corruption of the
glyphs and we appear to be retaining and reusing a deleted GDI font
handle which is a plausible reason for the crashes on other peoples
setups.

So I propose b3ec98dea6e59dcc0c94aeece0e4f8e35430a86a for 3-6 which
fixes that. Patch might look a bit big, but the code logic is unchanged
before/after except that now when we scale the font down we throw away
the layout based on the unscaled font and make a new one, instead of
just changing the font of the device the layout uses.

C.