Problem: Attach-time terminal probes cannot distinguish responses from
different attached UIs.
Solution: Identify the UI by RPC channel id in `TermResponse` and make
`vim.tty.request()` filter responses by channel.
Problem:
No way to handle a "tab moved" event.
Use-case: tabline plugins may cache tab labels, and need to know when to
invalidate their cache.
Solution:
Add a `TabMoved` event that triggers whenever tabs are reordered via `:tabmove`
or via mouse click-and-drag.
Problem:
No LuaLS types for event-data fields (ev.data). Types are only
documented ad hoc in scattered locations.
Solution:
Add runtime/lua/vim/_meta/events.lua defining vim.event.<name>.data
classes for events that provide ev.data. Reference the types from
each event's help in autocmd.txt, lsp.txt, and pack.txt.
