Propagate clicks to RCE's window instead of to top
Propagate clicks to RCE's window instead of to top

Fixes MAT-923
flag=none

Test plan:
- Find an RCE
- Insert an equation
- Click "Edit Equation"
* Verify that the equation dialog pops back up
- Find an RCE inside a New Quizzes quiz
- Insert an equation
- Click "Edit Equation"
* Verify that the equation dialog pops back up
* Verify there is no "cross-origin iframe" related error in the console

Change-Id: I3b8a160999ecd8503b11bb835cbc2426604f0d4b
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/297799
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Joe Hernandez <2475ff9f2214a383ad29b079daec0de5f5df5945@instructure.com>
QA-Review: Joe Hernandez <2475ff9f2214a383ad29b079daec0de5f5df5945@instructure.com>
Product-Review: Jon Scheiding <9af6aa5061dd5eef0e85122953253a66930fcf3e@instructure.com>

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