Add OSC8 hyperlink support

[zedinosaur]

Per the specification described in https://gist.github.com/egmontkob/eb114294efbcd5adb1944c9f3cb5feda, add hyperlink support to mosh.

Closes #1245

[achernya]

For us to consider merging this it needs to have test coverage.

[zedinosaur]

That's a fair cop. I didn't immediately find the test suite but now I have I will take a crack at it.

[zedinosaur]

Good catch. I'm rethinking the way the params are parsed and they should all be technically preserved, not just id.

[zedinosaur]

PTAL, there's a test now and I reworked the param parsing.

[zedinosaur]

Please let me know if there's any further issue. I'd like to take a stab at adding OSC7 support as well since it seems straightforward compared to this, but would like to see this merged first.

[eminence]

I did a quick test and review and it seems to work as advertised, but I'll do some more real-world testing over the next few weeks

[eminence]

I'm doing some testing with ripgrep, which has support for OSC 8 hyperlinks. In particular there's a special "vscode" mode that causes some problems.

echo test > test
rg test -g test --hyperlink-format=vscode --color=always

In my terminal, it looks right:

But when I clear my terminal, I see some underlines left over:

This doesn't happen outside of mosh.

You can also test with this:

printf "\e]8;;vscode://file/home/achin/test:1:1\e\x5c\e[0m\e[35mtest\e[0m\e]8;;\e\x5c:\e[0m\e[1m\e[31mtest\e[0m\n"

[zedinosaur]

Thanks for the review. I missed clearing the hyperlink correctly in Cell::reset(), fixed now. PTAL.

[zedinosaur]

Please let me know if you found any other problems, would love to see this merged.