Expanding/collapsing a node in the Explorer re-renders the whole workbench

[pcdavid]

This is particularly visible when a large diagram is opened.

1. Open a project with two diagrams, one small (S) and one big (B).
2. Open S, select a element in the explorer.
3. Expand/collapse the element in the explorer, not changing the selection. The effect is immediate.
4. Open B instead of S, and repeat step 3, expanding/collapsing the same element. It is now very slow.

There is no actual selection change, but since SelectionContextProvider's setSelection does not check that it calls setState with a new selection objet structurally equivalent but different in terms of identity. Now that the selection context is high in the component hierarchy, this re-renders the whole workbench, including the big diagram.

The solution is the same as in d995d6e: update the selection state if the key is new value is really structurally different from the previous one.

[AxelRICHARD]

This issue is reopened because the corresponding commit has been reverted by #3646