Add Custom TitleView

[beebls]

Please tick as appropriate:

• I have tested this code on a steam deck or on a PC
• My changes generate no new errors/warnings
• This is a bugfix/hotfix
• This is a new feature

Description

This is an addition that allows plugin developers to change the titleView of their plugin. Currently, it is just a <div style={{ flex: 0.9 }}>{activePlugin.name}</div>. If a plugin has the titleView prop in their definePlugin return value, it will now display that instead of the boilerplate name.

This does not allow for removal of the back button, as that is crucial to ensuring people can exit out of plugins, the custom titleView slots in to the right of the back button.

[PartyWumpus]

Changes look good, but should probably be tested by someone before being merged

[PartyWumpus]

Tested and it works fully.