Fix external link not hidden

[cjrace]

Brief overview of changes

After releasing the last version with external_link() we found a couple of bugs with the add_warning = FALSE version of the link.

Why are these changes being made?

Hidden text was not being hidden. Excess whitespace was being added. We had missed this in the tests.

Detailed description of changes

• Attach CSS to the function to hide the hidden text.
• Crudely paste and reparse the HTML to work around the whitespace issues with htmltools::tags.
• Updated main package tests, and added some examples and tests to the test_dashboard.
• Added some extra info into the documentation as suggested by @jen-machin.

Additional information for reviewers

zzz.R is apparently a specific standard file name for that kind of on package load function. shinyGovstyle uses and copilot independently also said this was the case (which was enough for me to just do it, feel free to verify this further!).

Issue ticket number/s and link

#47

[cjrace]

Fix bug in external_link()

[jen-machin]

I have not spent a huge amount of time looking at every line of code but I have tested that everything works as it should 😄 thanks for the documentation updates!

[cjrace]

Done a quick double check on the zzz.R thing and that is definitely a standard - https://r-pkgs.org/Code.html#when-you-do-need-side-effects

If you use .onLoad(), consider using .onUnload() to clean up any side effects. By convention, .onLoad() and friends are usually saved in a file called R/zzz.R. (Note that .First.lib() and .Last.lib() are old versions of .onLoad() and .onUnload() and should no longer be used.)