[FIX] owselectcolumns: Fix performance on filtering with selection

[ales-erjavec]

Issue

Select Attributes has severe performance degradation on filtering a long list of variables (in the Available view) when all the variables are selected.

For example:
File ('geo-gds360') -> Select Attributes
move all variables to Available view, press Ctrl + A and enter any text in the Filter

Description of changes

• Coalesce the calls to update_interface_state using a single shot timer.

Includes

• Code changes
• Tests
• Documentation

[codecov-io]

Codecov Report

Merging #3030 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3030      +/-   ##
==========================================
+ Coverage   82.19%   82.21%   +0.01%     
==========================================
  Files         335      335              
  Lines       57688    57683       -5     
==========================================
+ Hits        47417    47422       +5     
+ Misses      10271    10261      -10

[lanzagar]

Improves filtering, but just to ask - how hard would it be to speed up drag and drop too? Dragging all features to Available in geo-gds360 takes a looong time.