Login error handling accessibility improvements

[afercia]

Splitting this out from #29955

As reported:

When the user attempts to login with incorrect login information a message appears on the screen, “ERROR: The password you entered for the username admin is incorrect. Lost your password?” This statement is not made available for JAWS to announce automatically.
Expected result: All dynamically appearing messages are expected to be made available for JAWS to announce.

Proposed patch could be a simple way to have error messages automatically announced after page refresh. Given that the login form fields receive focus on page load, their aria-describedby would be automatically read out.

Would like to ask the accessibility team their feedback and availability for testing. Tested with Firefox + NVDA, seems error messages are read out correctly.

This solution could be used also for the other login forms: lost your password, reset password, etc.

Moved also two question marks, small detail in order to have screen readers read out text with a proper tone.

Aside:
having the form fields focused with JavaScript conflicts with the browser trying to focus on the "Would you like to remember the password..." built-in popup, at least in Firefox. A bit annoying for keyboard users.

[rianrietveld]

Results WPa11y test team:

Tina Tedesco
Screen reader: JAWS 15
When I put in a wrong user name and password, my screen reader did relay the error message properly, clearly and understandable.

@badeyes
Screen reader: NVDA 2011, IE11, Windows 7
Tested the login with incorrect username and password and noticed a big difference between the the nightly build and the one with the patch, the incorrect one (nightly build) left me wondering what happened but the fixed one read it out right away. Excellent!!

@cheffheid
Screen reader: NVDA
Looking and sounding good! NVDA reads out the error text. It doesn't notify me that "Lost your password" is a link though (for some reason). It sounds more like a taunt now.
It's particularly annoying because Chrome seems to like to focus on the first input field when a page is refreshed, meaning I need to shift-tab to get to a link I may not even realise is there.

Petra de Jong
Screen reader: Supernova
I got a decent warning what went wrong with the login:
wrong username, wrong password, no password given, etc.

Susan Grossman
Screen reader: JAWS
The aria-describedby attribute in the password input field is working fine. It reads the password field information and then it reads the error message.

[joedolson]

@drew @johnbillion Per conversation on slack, is there any reason these can't be committed? I haven't checked whether the patch needs a refresh, but I can take care of that if necessary. The user feedback was very positive, so I think this would be valuable to add.

[joedolson]

In my opinion, this is a bug. While it's true that in the current model, this information is available, with some effort on the part of the user, the log-in process is an aspect of the user interaction with WordPress that's crucially important, and needs to be as smooth for all users as possible.

[johnbillion]

In 31871:

Implement an aria-describedby attribute for login screen errors, and improve the "Forgot password?" anchor text.

Props aferica, rianrietveld
Fixes #31143