Menus stay highlighted/open when they should lose focus

[benjiwheeler]

@seotts reports:

If I press “Load from your computer,” choose a file, and then press cancel on “replace contents of project”, the “File” button in the menu stays dark blue until I click elsewhere (this might be only on Chromebook)

@kchadha reports:

On Mac Safari, File menu stays open after starting to load a project and pressing cancel in the file picker

We should do an audit of how these behave on multiple platforms/browsers, in multiple situations, and see if we can get these working more consistently.

Help Wanted
The most helpful contributions at this point would be to help document the behavior in different situations. Using the steps below, please add comments that include:

• Device information: Ideally manufacturer and model, e.g., Apple Macbook Pro (2018), or HP Chromebook x360
• Operating system and version
• Browser and version
• What happens to the file menu when you cancel file upload or replacing the project contents. Is the menu still open or closed, is part of the menu highlighted or not? screenshots are encouraged.

Steps:

1. Open a new project in the Scratch Editor
2. Click File...Load from your computer...
3. Click cancel in file picker

Repeat steps 1-2, then:

3. Chose a file and click ok
4. Click cancel in response to the "replace contents of this project" prompt

[apple502j]

Related to #4681 - it's hard to detect when "cancel" is pressed