Search UI: revamp expand/collapse functionality for repo sidebar

[jasonhawkharris]

Before, UI for collapsing/expanding the sidebar was awkward and required too many additional mouse movements to toggle back and forth. Now, the toggle button is static, stays in the same place, and is integrated more solidly into the UI.

Before:
https://github.com/sourcegraph/sourcegraph/assets/62355966/e2fafd2e-2098-465a-8509-18d03bccae19

Now:
https://github.com/sourcegraph/sourcegraph/assets/62355966/b0dd793a-0dca-40f3-b52c-7f15d4ec4263

Test plan

Manual/Visual testing
Ships with passed unit tests
Ships with passed e2e tests

[sourcegraph-bot]

📖 Storybook live preview

[vovakulikov]

@jasonhawkharris with these new changes I think there is a state where you can't open a file tree as it was before, check the repository page on folder or just on root page, previously there was a sidebar button that allows you to expand the file tree

Screen.Recording.2023-10-13.at.14.42.35.mov

[jasonhawkharris]

@jasonhawkharris with these new changes I think there is a state where you can't open a file tree as it was before, check the repository page on folder or just on root page, previously there was a sidebar button that allows you to expand the file tree

Screen.Recording.2023-10-13.at.14.42.35.mov

@rrhyne regarding the bug @vovakulikov brought up here. Do you have any ideas about where to place the fixed button when in project view? Maybe oriented to the left of the repo/branch info?

[taiyab]

@jasonhawkharris

Thanks for this. Great effort! :)

Thoughts on consistently keeping it at the start of the navbar in all contexts?

cc @vovakulikov

[vovakulikov]

@taiyab no big objections about having it before repo and commit buttons from my side, I remember there was an argument from Rob (and I think I can relate to this) that this button opens something below kind of becoming disconnected to actual file tree sidebar in this case.

My reckless initial idea was always having a separated column for this button (the whole row is clickable and opens/expands the sidebar panel), got this idea from google code search and JetBrains IDE.