Support goto symbol navigation

[ctheune]

After reviewing issues and discussions I think this hasn't been brought up before. It does hamper my workflow quite a bit:

Sublime's open palette supports navigating deeper into files.

<filename>:<lineno>

but also for symbols:

<filename>@<symbol>

Would love if this could make it into Zed.

[ctheune]

This might be related to #13307