#a11y-headings - the FTP credentials screen and modal headings

[afercia]

The FTP credential screen and modal dialog display (conditionally) some headings:

'Connection Information' <-- h3
'Authentication Keys'    <-- h4
'Connection Type'        <-- h4

• when displayed in the Updates screen they're inside an iframe, which technically is a separate document, so the first heading should be a H1 but this wouldn't make much sense for the overall headings hierarchy
• when displayed in the modal dialog, the first heading should be a H1 because for assistive technologies the dialog content is the only available content on the screen (it has an ARIA role=dialog and keyboard navigation is constrained within the modal)

About the second and third headings, I'd propose to change them in fieldset legends. That seems the most semantic markup to me.

Not sure what to do with the first heading, would appreciate some feedback. Any thoughts more than welcome.

#a11y-headings

[afercia]

A couple of screenshots for reference, please notice some form sections are displayed conditionally depending on the authentication type:

the FTP credentials form when updating from the Updates screen:

the FTP credentials modal dialog and form when updating from the Plugins screen:

So, in the first case "Connection Information" should be a H2 but in the second case (within the modal) a H2 wouldn't make much sense.

[afercia]

Attached patch is a first pass, waiting for some feedback about the "Connection Information" heading which is now a H2. The other two headings are now fieldset legends. See screenshots with the patch applied below, there are just a few pixel differences about the legend margins, not sure we should try to fix them I'd rather keep it simple.

[afercia]

Refreshed patch, added a simple way to conditionally print out the heading as a <h1> in the credentials modal dialog and as <h2> in the updates screens. Tweaked and moved styles to forms.css.

[wonderboymusic]

In 35315:

Plugins/Updates: in request_filesystem_credentials(), alter the heading HTML tag based on the current screen for improved semantics.

Props afercia.
Fixes #34267.