[Enhancement] Shell TItleBar(?) text with tabbed and non tabbed content

### Description

The Shell content titlebar(at least I think that's what it is) at the top, underneath the main titlebar(what are the plans for this with desktop apps btw?), should display differently according to what content is being displayed. When using Tabbed content, Tab uses the title of the first ShellContent page as the title text. I'm not sure if that's intended behavior, or a bug, but I feel like with Tabbed content, the title should be the FlyoutItem's title. Using the ShellContent page titles is redundant. The name of the first page will be in the titlebar AND the tab text. When the content of a FlyoutItem is just a single page, that would make sense to use the page's title, but in reality, it should still use the FlyoutItem's title. Feel free to guide me, but isn't the purpose of the titlebar to be in correlation with the FlyoutOut, or no?

A work around for this, is to name every ShellContent's Page.Title in my FlyoutItem the same name as the FlyoutItem.Title, and then it's 100% the way I think it should be. Open to any criticism and comments by all means.

Also, is it possible to change the titlebar color from black?

Example:

### Public API Changes

n/a

### Intended Use-Case

n/a