Support for differentiating the tweak tool from the 3D cursor when
select is set to RMB.
This is currently an experimental preference:
Tweak Tool: Left Mouse Select & Drag
When enabled the tweak tool can now tweak the existing selection
without de-selecting first, a single click can be used to replace
the selection.
This matches selection in the graph & node editors.
This preferences is only available with "Developer Extras" enabled.
Ref T96544.