Preserve URLs in links

[nholden]

In #288, @mrcljx pointed out that characters in link URLs that are already escaped get escaped again. For example:

<a href="https://google.com/a?x=y%3Az">show</a>

is encoded as

<https://google.com/a?x=y%253Az|show>

This PR removes implicit encoding from link URLs. Following @yhatt's recommendation, it ensures we continue to escape characters that Slack reserves. &, <, and > are replaced by corresponding HTML entities, and we continue to use urlEncode to escape |.

closes #288

[yhatt]

Thank you for your contribution 😄

The hyperlink with date formatting still has implicit URI encoding.

<a href="https://example.com/?x=y%3Az">
  <time datetime={1234567890}>{'test: {date_short}'}</time>
</a>

<!date^1234567890^test: {date_short}^https://example.com/?x=y%253Az|test: Feb 13, 2009>

In addition, ^ also should escape in the link with date formatting. If not, a hyperlink will truncate raw ^ character and after chars.

[nholden]

Thanks, @yhatt! Great catch.

I took a stab at addressing that in efed184. Looks good in the Block Kit Builder, but I'm open to other approaches!

[yhatt]

Looks good for me 😄

CI has failed due to vulnerability check of dependencies. I'll work on updation in another PR.