x/pkgsite: expand all should be collapse all when all directories are expanded

[julieqiu]

What is the URL of the page with the issue?

https://pkg.go.dev/cloud.google.com/go@v0.76.0#section-directories

What is your user agent?

Mozilla/5.0 (Macintosh; Intel Mac OS X 11_1_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.96 Safari/537.36

Screenshot

What did you do?

Clicked "Expand all"

What did you expect to see?

"Expand all" to change to "Collapse all"

What did you see instead?

"Expand all" without option to collapse.

/cc @jamalc

[julieqiu]

The "Expand all" toggle can also be omitted when there is nothing to expand. For example, on https://pkg.go.dev/net/http@go1.15.6#section-directories:

[Olament]

I am wondering what state the "expanding all" button should be when only some of the directories are expanded. Also, Do you expect the "expanding all" button changes to "collapse all" if I manually expanded all the directories?