Declare rectangle functions in mouse.el to avoid warnings

* lisp/mouse.el (rectangle-dimensions)
(rectangle-position-as-coordinates, rectangle-intersect-p):
Declare these functions from rect.el to avoid compilation warnings.
1 job for master in 90 minutes and 6 seconds (queued for 7 seconds)
Status Job ID Name Coverage
failed #1789


Name Stage Failure
test-all Test The script exceeded the maximum execution time set for the job
  ELC      lisp/gnus/message-tests.elc
GEN lisp/gnus/message-tests.log
ELC lisp/help-fns-tests.elc
GEN lisp/help-fns-tests.log
ELC lisp/hi-lock-tests.elc
GEN lisp/hi-lock-tests.log
ELC lisp/htmlfontify-tests.elc
Pulling docker image gitlab/gitlab-runner-helper:x86_64-f100a208 ...
ERROR: Job failed: execution took longer than 1h30m0s seconds