Experiment: keep stack of definitions in ref panel

Created by: mrnugget

1hr hack attempt to fix https://github.com/sourcegraph/sourcegraph/issues/30973. Lots of smaller issues here, obviously.

Demo

https://user-images.githubusercontent.com/1185253/189112105-6d22772c-09b4-40f2-ac76-59d16ad21989.mp4

Test plan

• manual testing but not all edge cases covered

App preview:

• Web

Check out the client app preview documentation to learn more.