This will need fixups, because the commit checker won't let me indent
a nested #define.

Hash mark must go in first column, as per https://wiki.openttd.org/Coding_style#Other_important_rules

Since they are only ever called with an int and a (int)uint; the
templating seems completely unnecessary and redundant.

This reverts commit 8652a4d.
This is necessary to aid in the cherry-picking of commits from JGRPP.

…g window list.

This is to speed up marking all viewports dirty, which is done very
frequently.

…acked for later redrawing

Track dirty viewport areas seperately form general screen redraws.
Maintain a dirty block grid per viewport, with a smaller block size.
Use even smaller block size in viewport map mode.

Use a rectangle array for general screen redraws instead of a block grid.

Add a dirty bit to windows and widgets, to simplify the common case
of repainting a whole window or widget, without catching
neighbouring windows or viewports.

…dler

AddDirtyBlocks is an internal implementation detail of SetDirtyBlocks,
and its name should reflect that.

The viewport cache is transparently managed by the ViewportData struct,
and memory associated with the viewport and cache is automatically
managed using smart pointers.