Focus tracking for input on web is janky

[jprochazk]

When running an eframe app on web, sometimes focus is not properly assigned to the hidden text <input> (referred to as "text agent" from this point on) which results in strange behavior.

So far we've observed:

• Selecting text in a mutable text field on any platform doesn't focus the text agent at all
• Clicking on a mutable text field sometimes doesn't work on iOS, MacOS, and Android