Show only core navigation buttons when widget is maximised

[jryans]

When a widget is maximised in a room, we should show only the core communication-focused room header items:

• call
• chat (added by Add main timeline chat in right panel when widget is maximised #19633 in this project)
• notifications
• info

This goal of this is reduce complexity and confusing that may occur when trying to use e.g. search at the same time. If we find this is quite strange via feedback and from testing the feature a bit, we'll revisit this.