Compositor: Initial support for canvas compositing

Compositor: Replace resolution concept by canvas

This is a code refactor in preparation of supporting canvas
compositing and fix all cropping issues on full frame implementation.

No functional changes, all canvases are at (0, 0) position matching
tiled implementation.

Merge branch 'master' into compositor-full-frame

Compositor: Fix crash enabling buffer groups on full frame

Full frame doesn't support this option as all operations are already
buffered. UI option will be removed in the future.

Compositor: Fix dilare erode reading input out of bounds

Happened when output area was partial horizontally, for example
when using a viewer border.

Compositor: Do not register constant input areas for rendering

If an input is only used as a constant it doesn't rendering
because its already calculated after constant folding.

Compositor: Fix plane distort operations incorrect areas of interest

The original implementation doesn't work for all cases.

Compositor: Fix plane track wrong area of interest calculations

Perspective matrix in sample data was not initialized because corners
were not calculated at that point of execution.

Compositor: Fix incorrect area of interest in variable bokeh blur

Compositor: Fix incorrect copying of uchar buffers

Row stride and the area x coordinate offset were not taken into
account.

Compositor: Enable can_be_constant on vector nodes

Compositor: Full frame Normalize node

Compositor: Full frame Normal node

Compositor: Full frame Map Value node

Compositor: Full frame Map Range node

Compositor: Enable can_be_constant on matte nodes where possible

Compositor: Full frame Luminance Key node

Compositor: Full frame Keying Screen node

Compositor: Full frame Keying node

Compositor: Full frame Distance Key node