Reintroduce feature to validate that CMS users have entered alt tags for images

[robbieaverill]

See https://github.com/silverstripe/cwp-core/pull/46

The cwp/cwp-core module has some logic which (in theory) is validating that an image added in the CMS has been given and alt tag (for accessibility).

In the context of CWP 2.x this doesn't work because the code hasn't been correctly upgraded from CWP 1.x and isn't actually being run in CWP 2.x at the moment because it's excluded by an incorrect config class namespace and the update hook it's using doesn't exist in core any more.

The feature still seems useful, so we should reintroduce it in this module rather than cwp/cwp-core which is designed for platform CWP support.

The old javascript does the following:

• Sets alt text to empty for upload items when the value is the defaultValue prop (not sure if this still exists)
• Asks the user to confirm that they're OK to add an image with no alt text when submitting an upload file form in the CMS
• Highlights any uploads in the form that have errors (using custom CSS changes in the javascript)

Side note: I'm raising this as a new feature rather than a bug because it hasn't existed in CWP 2.x at all yet.

[robbieaverill]

Re-triaged as a bug since it's missing functionality. This is duplicated by https://github.com/silverstripe/cwp-core/issues/55, which was also triaged as a high impact bug.

[brynwhyman]

There's talk of putting validation in the asset-admin module directly https://github.com/silverstripe/silverstripe-asset-admin/issues/840

[brynwhyman]

With the introduction of the enhancements made in https://github.com/silverstripe/silverstripe-asset-admin/issues/983 I'm going to close this issue.

The recent changes don't include validation that alt-text has always been entered, but I think that's appropriate. Alt text shouldn't always be required, so the focus should be on giving the Content Manager enough information to make an informed decision. The above issue does that.