Replace "title" attributes with "aria-label" in <a> tags

The first commit removes title attributes from <a> tags and replaces them with aria-label.

From accessibility point of view, the title attribute doesn't help the screen reader. Instead we should use aria-label. But it should be used only to describe the text. For example: <a href="">View</a> view what? We should use: <a href="" aria-label="View post">View</a>.

Blind people can't see the screen, this is why we use aria-label to add more info for screen readers.

On the other hand, this code: <a href="" aria-label="View">View</a> it has no meaning. It does not add more information.

Reference from WordPress core: https://core.trac.wordpress.org/search?changeset=on&q=Accessibility+Remove+title+attributes&page=2&noquickjump=1

In the other 5 commits I'm removing the title attribute from elements like <div>, <label> and <li>.

In some places we need to remove the title attribute, in some places move the title attribute to inner elements, and in other places replace it with screen-reader-only text.

Preview switcher:

Template library actions:

Edit tools for widgets/columns/sections:

The progress widget commit above is based on https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/ARIA_Techniques/Using_the_progressbar_role and several other similar resources.