Accessibility: "Toggle more information" buttons

[GaryJones]

Feedback given by @rianrietveld in #285 (comment) indicated that when buttons are extracted from their context (such as screen reader software can do), then they are not uniquely identifiable.

(Rian's image from 2017 - the specific button texts have changed now, but the point still stands)

The buttons currently use the aria-label approach, so instead of a fixed aria-label="Toggle more information" attribute, it should include a reference to the thing is will display more details about. For example:

• aria-label="Toggle more information about VaultPress_IXR_SSL_Client->query() caller", or
• aria-label="Toggle more information about Jetpack->add_configure_hook() hook callback".