For the main thread list search, we rely on the reordering behavior of getThreadListSearchResults to surface the most relevant results first (private and personal threads) when a user searches for a username.

This diff introduces similar functionality for ThreadPickerModal on both native and web. I considered trying to extract the reordering logic, but since it operates on ChatThreadItem and I needed to operate on ThreadInfo, this would have been messy. Instead I opted to duplicate it.

Note that on native, ThreadList is used in only two places. One of them is ThreadPickerModal, and the other is ComposeSubchannel, which doesn't use the searching functionality at all.

Depends on D12250

I tested by connecting my local simulator to the prod keyserver, logging in as a test user, and confirming that when I searched for "ashoat" in the ThreadPickerModal, the results were reordered so that the test user's PERSONAL thread with me appeared first