QtWebEngine confuses screen reader when regaining focus

(Theory of cause was: "QTWebEngine needs to implement QAccessibleInterface::focusChild to drill down to the inner most child. As things stand it always reports  the body as being the inner most child." but that doesn't appear to be the underlying cause).

To see the problem:

• build the "WebEngine Widgets Simple Browser Example" on Windows-10
• Start Windows Narrator
• Run the simplebrowser, and load https://gtritchie.github.io/focustest.html
• Use Tab key to move focus to the text input field on the page (named "Input One")
• Type "abcd"
• Move the caret with left/right arrows and observe how Narrator reads the characters
• Alt+Tab to a different program
• Alt+Tab back to simplebrowser
• Try using the arrows; the screen reader has been confused by incorrect reporting of the focus location
• If you use Tab then Shift+Tab to move focus off of and then back to the text field it starts working again

This is a serious problem both for Narrator and JAWS. Try this experiment again with Chrome, Edge, or Firefox, and observe the expected behavior.