Fix IDE editor to update dimensions on show change

What does this MR do?

This fixes a bug where the IDE editor would be invisible after switching to "edit" from markdown preview.

Before	After
20190628_before	20190628_it_works

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Links

• Fixes #45120 (closed)