rect: move IRect to rect.rs

It is used also outside of filters, so let's move it somewhere more
generic.
7 jobs for get-pixbuf in 25 minutes and 43 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Test
passed #176054
fedora test

00:06:54

 
  Lint
manual #176056
allowed to fail manual
clippy
passed #176055
rustfmt

00:01:19

passed #176057
tarball

00:10:23

 
  Cross Distro
passed #176060
debian_i386:testing

00:07:39

passed #176059
debian:testing

00:07:01

passed #176058
fedora:rawhide

00:08:23