viewer: Add composition guidelines

Composition guidelines are simple lines that help with framing and
position in an aesthetically pleasing way.

Added a new overlay class (that is not attached to a source) to draw the
composition guidelines. Also, add a menu in the viewer to select the
guidelines.

Fixes #2298
1 job for composition_guidelines_feature in 13 minutes and 29 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #698255
flatpak
build

00:13:29