UI: improve form-rendering

[klees]

Hello ILIAS-Community,

this is the result of my last open contract to work on the ILIAS core with you: Make a proposal to solve #43886 and #43899, which requires to improve the general structure of the Forms in the ILIAS-UI-Framework. The contract was budgeted by the ILIAS-Society (thanks @mkunkel and @oliversamoila).

Besides the requirements regarding accessibility, the implementation was guided by these requirements:

• For every input field there is a common set of "context" that needs to be represented:
  • label
  • byline
  • error message
  • the actual input element from html
• For every input that context should be as regular as possible:
  • to attach JS as easy as possible
  • to make styling via CSS as easy as possible
  • to make rendering code as simple as possible
  • to allow for easy maintenance of the template and all other code

Please keep in mind that this does not intent to solve each and every accessibility problem in the Forms (or in general ILIAS, of course). Some are carried along from previous versions.

To solve the requirements I had to rewrite and rewire most of the rendering code of the Form, which IMO looks like an improvement in its own right. Also, it should allow to make further improvements more easily. I checked the output regarding HTML-structure and accessibility with the IBM Equal Access Accessibility Checker in version 4.0.12. I'm quite confident that there are no open issues regarding my intended change set, but I might have missed some issues in the swath of other problems that the tool flags on each and every page.

From my POV this is currently good to go to check the new HTML- and code-structure. There are still open tasks, even regarding this change set:

• styling is broken in many places, it would also be advisable to adjust class names AFAIC
• some functionality needs to be reconstructed, most prominently the Optional and Switchable Group
• the unit test currently fail due to the changed HTML output

I don't think that these are worthwhile to work on, though, as far as the HTML structure is not approved by someone.

Please precede with this change set as you see fit.

Kind regards!