Fix QS edit accessibility.

- Announce the correct QS tile positions when moving/adding tiles.
- Only insert a placeholder tile when adding tiles.
- Ensure all tiles are draggable, even if they are currently unavailable.
- Fix off by one error adding tiles into the last position.
- Remove tile remove a11y announcement as it is unnecessary.

Change-Id: Ia0bc1cb1559c2e46f9ddfe0f3ba0f50d5de56868
Fixes: 78608195
Fixes: 78611593
Fixes: 74253408
Test: manual