(#347): Set the ink_rect of Pango layouts, not just their objectBoundingBox rect

The ink rectangle of Pango layouts was only being "grown" onto the
current bbox if the text was being rendered with a stroke.  We always
need a starting ink_rect, equal to the non-stroked bounds; we can grow
it later when needed.

This includes a new dimensions test for this issue.

GNOME/librsvg#347
3 jobs for <span class="ref-name">sub-positions</span> in 7 minutes and 43 seconds (queued for 13 seconds)
Status Job ID Name Coverage
  Test
passed #111925
fedora test

00:07:23

 
  Lint
manual #111927
allowed to fail manual
clippy
passed #111926
rustfmt

00:00:20