Problem
- `redir_exec` is obsolete, but it keeps getting used in new tests
  because people copy existing tests.
- Disadvantages of `redir_exec`:
  - Captures extra junk before the actual error/message that we _want_ to test.
  - Does not fail on error, unlike e.g. `command()`.

Solution
- Use new functions like `nvim_exec` and `pcall_err`.

Port VimL's method call syntax - vim-patch:8.1.{1638,1800,1803,1807,1809,1816,1820,1821,1828,1834,1835,1861,1863,1878,1879,1888,1909,1911,1912}

Problem:    More functions can be used as methods.
Solution:   Make a few more functions usable as a method.
https://github.com/vim/vim/commit/e49fbff384e45dd17fed72321c26937edf6de16b

Problem:    Only some assert functions can be used as a method.
Solution:   Allow using most assert functions as a method.
https://github.com/vim/vim/commit/24278d2407dfbc8d93eb36593cdd006ff5d86f94

Port tests to assert_spec.lua.

It might come as a schocking surprise, but the defaults we support
are the NEOVIM defaults.

Memory compression could complicate the measurements.

Problem:    The wininfo list may contain stale entries.
Solution:   When closing a window remove any other entry where the window
            pointer is NULL.
https://github.com/vim/vim/commit/4882d983397057ea91c584c5a54aaccf15016d18