Make pdf edge-to-edge and add logic to dodge window insets

[hunterstich]

👋 This change makes the PDF WebView always edge-to-edge, avoiding any jumps in the pdf's location on screen when hiding/showing system insets or app UI.

Resolves #273.
The AppBarLayout's show/hide animation could still be improved if that's something the project would like!

Summary:

• Draw PDF WebView under AppBarLayout by removing the scrolling behavior and correcting z-order
• Enable edge-to-edge with WindowCompat#enableEdgeToEdge(window) to make WebView draw behind insets. enableEdgeToEdge internally calls WindowCompat#setDecorFitsSystemWindows(window, false) which can be removed
• Add PDF canvas insetting based on system WindowInsets and the height of the AppBarLayout so all parts of a PDF can be scrolled into view regardless of system/app UI visibility

Before:

before_.pixel5_api34_withCameraHolePunch_480.mov

After:

after_pixel2_api28_480.mov

after_pixel5_api34_wCameraHolePunch_480.mov

[ggtlvkma356]

LGTM, thanks!

[inthewaves]

Actually, I just noticed #538 which seems to be more fleshed out (though marked as a draft)

[octocorvus]

I planned on submitting more changes along with #538 for review

[octocorvus]

The text layer alignment is fragile with the current approach. So, upcoming PDF.js updates and changes to code often breaks it. #538 also aims to improve the overall architecture by introducing a page element.

[hunterstich]

@octocorvus oh nice! Yea, just updated this PR to fix the text layer but it feels somewhat brittle. Having a page wrapper or similar to your PR seems like a nice approach.