[SuperEditor] Add more specific SelectionChangeTypes (Resolves #2367)

[angelosilvestre]

[SuperEditor] Add more specific SelectionChangeTypes (Resolves #2367)

Currently, when moving the caret using up or down arrow, the editor generates a selection change event with the type SelectionChangeType.collapseSelection. This makes it difficult for reactions to determine if the selection moved up or down.

Also, our SelectionChangeTypes for pushing the caret or extent don't carry the direction of the selection change.

This PR removes SelectionChangeType.pushCaret and SelectionChangeType.pushExtent in favor of more specific types:

• SelectionChangeType.pushDownstream
• SelectionChangeType.pushCaretUpstream
• SelectionChangeType.pushCaretDown
• SelectionChangeType.pushCaretUp
• SelectionChangeType.pushExtentDownstream
• SelectionChangeType.pushExtentUpstream
• SelectionChangeType.pushExtentDown
• SelectionChangeType.pushExtentUp

This is a breaking change, but I think it's much more safer to generate a compilation error instead of keeping SelectionChangeType.pushCaretUp and possibly silently failing at runtime.

The upgrade should be straightforward:

Before

if (selectionChangeType == SelectionChangeType.pushCaret) {

}

switch (selectionChangeType) {
  case SelectionChangeType.pushCaret:         
    break;
}

After:

if (const [
  SelectionChangeType.pushCaretDownstream,
  SelectionChangeType.pushCaretUpstream,
  SelectionChangeType.pushCaretDown,
  SelectionChangeType.pushCaretUp
].contains(selectionChangeType)) {

}

switch (selectionChangeType) {
  case SelectionChangeType.pushCaretDownstream:
  case SelectionChangeType.pushCaretUpstream:
  case SelectionChangeType.pushCaretDown:
  case SelectionChangeType.pushCaretUp:
    break;
}

// The same for pushExtent.

On Android, we are always generating a selection change type of SelectionChangeType.pushCaret. This PR changes it to SelectionChangeType.placeCaret, but it might be better to let that decision to the touch interactor instead.

On web, things are a bit trickier. We handle selection changes by IME deltas, so we don't have information about the intent of the selection change. Should we compare the new selection, with the selection that is expected when the user presses up/down/left/right arrow to determine what is the correct selection change type?

[angelosilvestre]

@JostSchenck Could you please try this PR to see if it works for you?

[JostSchenck]

@angelosilvestre Thanks a lot. Trying it out now, but will respond to the issue for the context there.

[JostSchenck]

@angelosilvestre This PR solves my problem, thank you very much.

[matthew-carroll]

I think I/we made these descriptions too verbose to begin with. There are so many words that it actually confuses the meaning.

Let's go with: "Move the caret one unit downstream."

Please attempt to adjust the other descriptions to have similar concision for the sake of clarity.

[angelosilvestre]

Updated.