force event placement recalculation when starting week calendar
force event placement recalculation when starting week calendar

test plan:
 - set the calendar to week view
 - load the page in a large browser window
   (may be a good idea to get into a state where this is
    reproducing consistently before pulling down the PS)
 - events should appear in the correct time slot (or quickly
   snap into this slot after the page loads)

sorta fixes LS-1213

flag = none

Change-Id: I79957a1ca6da9367a17058e3b21a84ab87991ab6
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/242789
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Alex Anderson <8690c85fe64134788579ce84d396a27368e019d5@instructure.com>
QA-Review: Robin Kuss <0b206b54367b2de0334896ea45826f0e3194bd35@instructure.com>
Product-Review: Jeremy Stanley <b3f594e10a9edcf5413cf1190121d45078c62290@instructure.com>

instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms