Fix swapped incoming/outgoing icons in call hierarchy view

Swap the icons so they show the current state instead of target state.
- When viewing incoming calls: show incoming icon (with "Show Outgoing Calls" title)
- When viewing outgoing calls: show outgoing icon (with "Show Incoming Calls" title)

This matches VS Code's convention where toggle buttons display the current
state icon with the action title being the target state.

Fixes the issue where the icon showed the opposite of what was being displayed.

Co-authored-by: jrieken <1794099+jrieken@users.noreply.github.com>