feat(lsp): redrawstatus on progress notifications

[mfussenegger]

Problem:

Currently users can include vim.lsp.status() in their statusline, but
they won't see status changes if the statusline isn't redrawn on progress updates.

The simple solution for that is:

autocmd LspProgress * redrawstatus

But that has the problem that the last message remains stale until
something else triggers a redraw. To fix the stale messages, users would
have to add something like this:

local timer = vim.loop.new_timer()
api.nvim_create_autocmd("LspProgress", {
  group = lsp_group,
  callback = function()
    vim.cmd.redrawstatus()
    if timer then
      timer:stop()
      timer:start(500, 0, vim.schedule_wrap(function()
        timer:stop()
        vim.cmd.redrawstatus()
      end))
    end
  end
})

That's quite complex.

Solution:

Call redrawstatus by default. To avoid redrawstatus() burst the calls
are debounced to 60 FPS.

[justinmk]

Do we need a debounce util?

[gpanders]

Is redrawstatus "cheap" if the statusline hasn't changed? Otherwise, this could be wasteful if the user doesn't use LSP status messages in their statusline (unless we include that by default too?).