Don't allow LTI tool to be larger than its modal
Don't allow LTI tool to be larger than its modal

This can make scroll bars disappear and make content inside the iframe
inaccessible.

closes PLAT-5641

Test plan:
- launch an LTI tool modal in the following ways. The LTI 1.3 test tool
  works for this because it has content that is taller than the modal,
  although you could probably inspect element and add content to make it
  taller too.
  - tool installed with link_selection -- goto modules, add an item,
    choose External Tool
  - tool installed in RCE context (note, when changing the height there,
    there may be 2 scrollbars sometimes, but I tried before this commit
    and the behavior was the same)
  - other places that support deep linking??
- inspect element on something inside the iframe and run the following
  in the JS console. The iframe should never be taller than the modal,
  meaning there should always be scroll bars and all content should be
  visible. (Note: after each call you may have to inspect element on
  something in the iframe again to get inside the context of the iframe
  page)
    parent.postMessage('{"subject":"lti.frameResize", "height":"10000px}', '*')
    parent.postMessage('{"subject":"lti.frameResize", "height":2000}', '*')
    parent.postMessage('{"subject":"lti.frameResize", "height":100}', '*')
    parent.postMessage('{"subject":"lti.frameResize", "height":"200px"}', '*')
Change-Id: Icf4b85b926e6acedf5873981e0bd15ef3d074d93
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/231859
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Weston Dransfield <e9203059795dc94e28a8831c65eb7869e818825e@instructure.com>
QA-Review: Tucker Mcknight <4b51b98c1d84aa97854d216bd061ce5d3eda8a28@instructure.com>
Product-Review: Evan Battaglia <e557ffdfc4b80aab44858030b0ae5370b86cb7b1@instructure.com>

sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,djbender/canvas-lms