Bump scroll delay in node editor up to 0.5 seconds.

Merge branch 'master' into node-scrolling-improvements

Add back some of the delay in node edge panning.

Fixed missing BLI_rect.h include.

Merge branch 'master' into node-scrolling-improvements

Merge branch 'master' into node-scrolling-improvements

Merge branch 'master' into node-scrolling-improvements

Increase default node scroll speed again.

With the zoom influence feature the max speed at
default zoom can be increased again.

Zoom influence factor for edge scroll speed.

This allows modifying the scroll speed based on the View2D zoom factor.
With influence 0.0 (default behavior) the speed will be constant in
UI space as before.
At maximum influence 1.0 the speed will instead max out in the view
space, i.e. scrolls slower in UI space when zooming out.
At intermediate values the zoom influence is proportionally reduced,
for example at influence 0.5 the view will scroll as if zoom factor is
half of the actual zoom.

This feature is used in the node editor to slow down scrolling a bit
when zoomed out.

Merge branch 'node-scrolling-improvements' of git.blender.org:blender into node-scrolling-improvements

Zero delay in node editor scrolling.

The delay is more useful for the outliner, where lists can become very
long and it makes sense to speed up scrolling over time.
For the node editor, where scroll speed is slow and distances relatively
short, reactive scrolling is more important.

Only reset the node view when links are cancelled.

Improvements to edge panning in the node editor.

- New operator property to toggle edge panning in the keymap.
This is disabled by default to avoid edge-panning in cases where it
gets distracting, such as adding a new node. Only the explicit
translate operator(s) (GKEY or drag) have this enabled now.

- Restore the initial view rect on edge pan cancel.
The initial view rect is now stored in the edge pan operator data.
When an operator with edge panning is cancelled it can now call the
UI_view2d_edge_pan_cancel function to restore the original View2D
rect.

Differential Revision: https://developer.blender.org/D11736

Restore the initial view rect on edge pan cancel.

The initial view rect is now stored in the edge pan operator data.
When an operator with edge panning is cancelled it can now call the
UI_view2d_edge_pan_cancel function to restore the original View2D rect.

Transform operator flag to opt-in to edge panning.

This is disabled by default to avoid edge-panning in cases where it gets
distracting, such as adding a new node. Only the explicit translate
operator(s) (GKEY or drag) have this enabled now.