Blender Git Loki

Fix several issues with recent node selection changes.

Root of the issue (beside lack of control over operators evaluation in
keymaps, since tools always get tried first), is that wurrent WM code
only allows one modal op to start from a single event (returning
`PASSTHROUGH` in that case is useless, WM code still considers event as
consumed and does not try any further handling of it).

Solution is then to change trigger events of resize/link operators from
`LEFTMOUSE` to `EVT_TWEAK_L`, which makes more sense anyway, imho, for
drag operations...

Fix T64693: Can't resize selected node.
Fix T64933: "Dots" in node editor can no longer be selected by just clicking on them.
Fix T64660: no access to node connectors when a node is inside a layout frame.