Layout fixes to BetaFeatures

* Fix vertical alignment of title, checkbox and links
* Fix vertical alignment of description and screenshot
* Simplify HTML of links (only one element needed, not 2 or 3)
* Add label text for info link to match discussion link
* Fix logic to check link text is non-empty, rather than just set
* Update and tidy-up tests

Bug: 54925
Change-Id: I3cfb2149ec182175da2fbdeab86a2888da46bf94