Hi-DPI patches for 4.2

[Keith Curtis]

Perhaps it would be good to have Norbert double-check his work, but it
seems logical the later changes aren't necessary without his first
retina change to turn off auto-doubling mode, which is not a part of
this set.

Norbert is still in the investigation phase, and there are multiple
ways to implement this on the Mac, so there is no need to optimize for
cleanliness until it works. It should be put in the release notes that
this is for Linux and Windows only as Mac will still run in
compatibility mode.

Doubling bitmaps is a "hack" but since bigger bitmaps don't exist, it
is better than doing nothing. I haven't looked into the low-level
resource loading code, but there are very probably VCL changes
required once those new bitmaps are created. Once that happens, then
the doubling code can be removed, but only at the end, and it might be
a while given how many bitmaps exist in all the icon packs out there.

-Keith