filter region handles should work with all filters

What happened?

The size of the filter region can now be adjusted by dragging on two new diamond-shaped nodes with the node tool. This is especially useful for blur filters, whose area has been affected by a transformation of the filtered object. is not working on filters.

What should have happened?

should have on all filters

Inkscape Version and Operating System:

• Inkscape Version: 1.0alpha2 (c8c55c6, 2019-08-12)
• Operating System: windows 10
• Operating System version: 1809