Problem Bank "Add Components" modal is way too long in unit page iframe.

[bradenmacdonald]

If you have a unit with many components and a problem bank on the NEW MFE unit page (with an iframe), clicking "Add Components" will open a modal that's way too tall.

This only affects the new unit page, not the legacy page.

Note that we are planning to overhaul this workflow in #1096 but that work is delayed until we get more use feedback.

[navinkarkera]

@bradenmacdonald Should we intercept the Add components button click and open the modal in MFE similar to #1464. I am almost done with #1464 and this should be similar.

[bradenmacdonald]

@navinkarkera If it's an easy change, I think that would be a nice fix.

[navinkarkera]

@bradenmacdonald Yes, we can show the modal on MFE side and still handle the adding blocks part in legacy by sending message to the iframe.

[navinkarkera]

@jmakowski1123 @lizc577 @sdaitzman @marcotuts This is ready for AC testing on the sandbox