click_handlers: Prevent compose opening when copying code blocks.
click_handlers: Prevent compose opening when copying code blocks.

Previously, clicking the codeblock copy button also
triggered the compose box to open.

This is because of the fact that ClipBoard.js lacks the
ability to stopPropogate the event when clicked.

Rectified by explicitly defining the copy click event
within `is_clickable_message_element`, which disallows
the triggering of reply box.

Effectively a workaround for
https://github.com/zenorocha/clipboard.js/pull/475.

Fixes #17861.
eeshangarg/zulip,kou/zulip,hackerkid/zulip,kou/zulip,rht/zulip,hackerkid/zulip,zulip/zulip,andersk/zulip,punchagan/zulip,punchagan/zulip,punchagan/zulip,rht/zulip,zulip/zulip,kou/zulip,zulip/zulip,zulip/zulip,kou/zulip,zulip/zulip,eeshangarg/zulip,kou/zulip,eeshangarg/zulip,punchagan/zulip,hackerkid/zulip,zulip/zulip,punchagan/zulip,eeshangarg/zulip,rht/zulip,kou/zulip,eeshangarg/zulip,andersk/zulip,andersk/zulip,kou/zulip,punchagan/zulip,andersk/zulip,eeshangarg/zulip,hackerkid/zulip,hackerkid/zulip,zulip/zulip,rht/zulip,andersk/zulip,punchagan/zulip,hackerkid/zulip,hackerkid/zulip,rht/zulip,rht/zulip,andersk/zulip,eeshangarg/zulip,rht/zulip,andersk/zulip