Encode brackets in URI to avoid conflict with markdown links.

[tommyip]

This works for brackets in both stream and topic names.

Fixes #12579.

[zulipbot]

Hello @zulip/server-markdown, @zulip/server-message-view members, this pull request was labeled with the "area: markdown", "area: message view" labels, so you may want to check it out!

[timabbott]

A couple requests:
(1) Can you add a test for this?
(2) Are we confident that's the only syntax we need to encode? I'm wondering a bit whether we want to just do general URL-encoding here.

[tommyip]

@timabbott the link is already URL encoded, see hash_util.by_conversation_and_time_uri. We need to encode brackets here since they are valid URL symbols, but interferes with the markdown syntax.

I will add the tests.

[tommyip]

Added test. Also moved the encoding code out of the ClipboardJS constructor for easier testing.

[timabbott]

Awesome, merged, thanks @tommyip!