drawing_ctx: add ink_rect getter

This removes the last use of RsvgBbox outside drawing_ctx
3 jobs for bbox in 4 minutes and 32 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Test
passed #49602
fedora:test

00:04:10

 
  Lint
manual #49604
allowed to fail manual
clippy
passed #49603
rustfmt

00:00:22