Adjust aria roles and labels for collection search

[nngu6036]

This PR adds an aria-label to the search input, changes the input type to search and changes the search form to a role of search rather than form.

• The search role is a best practise for search forms.
• The input search type has no functional change, but can be styled differently by the browser.
• I would like to make the title mandatory to ensure CMS users accurately describe what is being searched. But the behaviour for this PR is that If no title is provided, it should fallback to "Contents search"

This is certainly an improvement for users of assistive technology as it will announce it is a search rather than just a generic input (and screen-reader users will have it announced as a page landmark), however, some user testing should ideally be done in the future to find out if the markup is too explicit.

Todo

Add the fallback if no title is provided

[JeffersonBledsoe]

@djay If we add an aria-label/ aria-labelledby to the search input, is the placeholder text even required, it seems superfluous. For example, VoiceOver reads the input in the following format: Input name input placeholder, search text field. This ends up being search Search, search text field for a portlet with a title of Search, which is fairly confusing to me.

I propose having the input labelled by the portlet title rather than hard-coding aria-label="Search". This allows for multiple languages as well as customising the label of the search input. The input would be read as filterTitle, search text input then, which seems clearer to me and still help meet WCAG SC 1.3.1 and SC 4.1.2 out-the-box. It would appear follows.

Barceloneta enabled:

Raw content:

[djay]

I think its better if there is a way to backdown to something still compliant should the user choose to not have a title.

[JeffersonBledsoe]

@petschki @djay As part of this PR, I'd like to make it easier for CMS users to meet WCAG without having to think about this. Part of that would mean ensuring that the search input always has a label. While I could add fallback aria-label of something like "Contents" (not just the word search as the screen reader should now announce being focused on a search and to help ensure it doesn't conflict with the global search), this isn't really meaningful to the context the search is being used in. For example, a search across a collection of medical records should have something along the lines of "Medical records" as it's label, so it is announced as "Search, medical records".

How would you feel about making the portlet title mandatory (to ensure we get a meaningful input description), but having a checkbox to visually hide the title to preserve styling options collectionfilter users may have already made? An upgrade step should be able to automatically enable this checkbox for anybody who has left the portlet title empty in the past/