[web] Use react-window

Summary:
Part of ENG-3976
This diff uses react-window package to render only visible threads. react-virtualized-auto-sizer is the recommended utility to automatically set height of the VariableSizeList. react-window works by applying a style to each element with an absolute position that it calculated.

There's one issue that I'm aware of: if you scroll down, the search bar will stop rendering and lose focus (but it will keep it's contents). On 1-1 with @ashoat we decided that's good enough for now. I will create an issue explaining a possible solution with docking the search bar before landing this diff.

Adding ashoat as reviewer because of new dependencies.

Test Plan: Check if thread list looks the same, and scrolls correctly. Try searching chat and check if everything works correctly. Check if an empty background tab renders correctly.

Reviewers: inka, kuba, kamil, ashoat

Reviewed By: ashoat

Subscribers: tomek, ashoat

Differential Revision: https://phab.comm.dev/D8234