This commit adds an aria-label attribute to cooked hashtags using
the post/chat message decorateCooked functionality. I have just used
the inner content of the hashtag (the tag/category/channel name) for
the label -- we can reexamine at some point if we want something
different like "Link to dev category" or something, but from what I
can tell things like Twitter don't even have aria-labels for hashtags
so the text would be read out directly.
This commit also refactors any ruby specs checking the HTML of hashtags
to use rspec-html-matchers which is far clearer than having to maintain
the HTML structure in a HEREDOC for comparison, and gives better spec
failures.
c.f. https://meta.discourse.org/t/hashtags-are-getting-a-makeover/248866/23?u=martin
fc199d42fa