remove CursorNode, fix pod center-on-selection

[lihebi]

Two changes:

• 458 introduced a changing behavior: selecting a pod will trigger a centering event. This PR removes that behavior. Centering event is triggered by state.setCenterSelection(true)

• state.CursorNode (introduced in #431) has been confusing with state.SelectedPods. We mentioned that we want to unify the two in https://github.com/codepod-io/codepod/pull/431#issuecomment-1665767266. Therefore, this PR removes CursorNode to use only SelectedPods.

[lihebi]

Merging, FYI @senwang86

[senwang86]

• It used to have an issue by using SelectedPods since 1) it doesn't record the order of selection, and 2) it mixes the "single-selection" and "multi-selection". It might be the reason of the following bug,
  1. Mouseclick ScopeB
  2. Left arrow key, which goes to ScopeA
  3. Shift + Down arrow key, which goes to the first child of ScopeA
  4. Esc should go back to ScopeA, but it went back to ScopeB

[lihebi]

4. Esc should go back to ScopeA, but it went back to ScopeB

Why Esc goes to parent? Do you mean shift+up?

[lihebi]

There shouldn’t be selection order problems, as there is only one pod being selected in the entire process.

[senwang86]

4. Esc should go back to ScopeA, but it went back to ScopeB

Why Esc goes to parent? Do you mean shift+up?

Oh, my bad, forget that we don't use Esc during jump.

[senwang86]

There shouldn’t be selection order problems, as there is only one pod being selected in the entire process.

What would happen if you use keyboard to jump after you multi-select pods?

[lihebi]

It’s straight forward to determine the target pod by proximity. Then a jump should first reset the selection, then select the target pod.