Xournalpp: Pinch to zoom is laggy

[coldspark29]

Affects versions :

• OS: Manjaro
• (Linux only) Desktop environment: X11
• Which version of libgtk do you use
  gtk3 1:3.24.14+9+g429a6287e0-1
  gtk2 2.24.32-2
• Version of Xournal++: 1.1.0+dev 46a4dc82
• Installation method: AUR

Describe the bug
Zooming is generally laggy using the new input system. Not tested if the old input system behaves differently.

[Technius]

This is likely caused caused by the canvas widget having to resize on document changes. I'll see I can fix it in the upcoming viewport refactoring.

[coldspark29]

Will you maybe also be able to fix the weird shifting to the side when zooming in?

[Technius]

I'll look into it; the goal is to overhaul the current zoom/layout spaghetti code so that it's easier to fix these kinds of issues.