add NavigationPage

[d-loose]

2023-01-09.17-27-57.mp4

I'll add some widget tests in a separate PR

Pull request checklist

• This PR does not introduce visual changes, or
  • I ran flutter test --update-goldens and committed the changes if there were any, or
  • I added before/after/light/dark screenshots if the visual changes I made were not covered by golden tests.

    	Before	After
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    Dark

[Feichtmeier]

Thank you @d-loose

Just for the sake of consistency, could use YaruBackButton for the leading widget?

[jpnurmi]

Sorry, I can't help myself but there's something inconsistent that stands out :D

[d-loose]

Naming things is certainly not one of my strengths 😆
YaruNavigationPage is an actual widget though - this page showcases the navigation in both YaruNavigationPage and YaruMasterDetailPage, depending on the "compact mode" setting. I wouldn't mind calling it YaruNavigationPage though.

[Feichtmeier]

🤷 yeah just change it xD For a moment I thought you mean NaviGationPage to match the camel case line xD

[jpnurmi]

Or maybe we could call it YaruBackButton :)

[Feichtmeier]

The GitHub cloud ☁️ helpers have a bad day. Container for the flutter snap test always hangs. Restarting