go-types
Go Types View adds a list of all types in the currently active file in a panel to the left of the screen. The panel is updated after each save, and has click-to-navigate functionality.
- Click
By Line(default) to sort entries by line - Click
By Methodto group types with their method, overriding line numbers. - Click a method, type, or declaration to navigate to that declaration.
Toggle open/close with option-ctrl-o (unless there's something else with that, then open with cmd + shift + p and search go types to toggle)

Being a newly published package, it's not bullet-proof yet. If you have any issues, I welcome Github issues and will fix it as soon as I can. Typically the following day.
Also keep an eye out for updates.