Addresses #1976 by implementing click->hold to rename for the project tr...

...ee.

This only implements hold->rename for the project tree. In digging into the working set it seems like it's a bit of an edge case because the inlineRename doesn't touch the working set, it just jumps to that file in the project tree and invokes the inline rename there.

I felt like this was the more common case. It may not close the bug altogether, but at least it's a start.
It's probably harmless to call `clearTimeout(null)`, but it would be a bit nicer to check `if (_mouseupTimeoutId !== null)` here.