This updates the behaviour for swapping the forward & share buttons such that they are all added to the toolbar's actionButtons list and simply swap isHidden to control visibility. This fixes the issue where the share button wouldn't alpha out during interactive toolbar visibility transitions

Resolves brave/brave-browser#50645

Test Case

• Load some webpage that can scroll
• With share button visible, verify that when scrolling down & up a page slowly the share button disappears and reappears with the rest of the items
• Tap a link on a page then tap back to make the forward button appear
• Verify that when scrolling down & up a page slowly the forward button disappears and reappears with the rest of the items