Fix "ref-issue" handling in markup

[wxiaoguang]

This is a follow up for #35662, and also fix #31181, help #30275, fix #31161

[wxiaoguang]

The "loading" state is still useful.

When I use GitHub, when my network lags, there is no UI response (no loading) when I hover the issue links, it looks unclear to me.

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[Yakov5776]

The "loading" state is still useful.

When I use GitHub, when my network lags, there is no UI response (no loading) when I hover the issue links, it looks unclear to me.

GitHub doesn't highlight the issue if it doesn't exist though, so how does it look unclear?

As seen here:
Yakov5776/symlink-tests#1

[wxiaoguang]

The "loading" state is still useful.
When I use GitHub, when my network lags, there is no UI response (no loading) when I hover the issue links, it looks unclear to me.

GitHub doesn't highlight the issue if it doesn't exist though, so how does it look unclear?

I mean when my network lags, I didn't change the "issue not exist" case, it can be optimized separately.