* preserve fields from LSP diagnostics via adding a user_data table to the diagnostic, which can hold arbitrary data in addition to the lsp diagnostic information.

This fixes the handler signature and also prevents n+1 requests firing
if there are multiple clients.

(The first `prepareCallHierarchy` handler is called once per client,
each invocation used `buf_request` to make more requests using *all*
clients)

Some parts of LSP need to use cached diagnostics as sent from the LSP
server unmodified. Rather than fixing invalid line numbers when
diagnostics are first set, fix them when they are displayed to the user
(e.g. in show() or one of the get_next/get_prev family of functions).

* feat(diagnostic): add vim.diagnostic.match()
  Provide vim.diagnostic.match() to generate a diagnostic from a string and
  a Lua pattern.
* feat(diagnostic): add tolist() and fromlist()

When vim.diagnostic.config() is called, the decorations for diagnostics
are re-displayed to use the new configuration. This should only be done
for loaded buffers.

- Fix the cursor position after applying TextEdits
- Support reversed range of TextEdit
- Invoke nvim_buf_set_text one by one

vim.diagnostic._set_signs doesn't return anything, so checking the
return value will always fail.