Selectable Lazy Column Refactoring

[fscarponi]

Due to SelectableLazyColumn usage, we found the following points that can be improved:

• [ ] SLC should directly handle the background color behaviour, so we need to introduce the SLCStyle (like we do inside the LazyTree) #158

• [ ] Selection appearance is clipped round the edges of each element selected, but in the IDE, continuous selection is not clipped between elements

• [ ] There are some possible issues with performance that probably can be solved by using different approaches. (info)

[fscarponi]

This issue will also solve:

100

158

[rock3r]

Closing as obsolete.