Refactor taskbar divider view to IconButtonView

- Breakout CL part 1
- This is a breakout cl from ag/24272821 to make it more readable and atomic.
- This cl consist refactoring of Taskbar Divider Line to be using IconButtonView.

Test: Manual, Visual
Bug: 265170176
Flag: ENABLE_TASKBAR_PINNING
Change-Id: I6719dd568986dce7cf9cdf0f287c3f079fd35ba6