Add terminal filtering and lastused to :ls (vim-patch:8.0.1651)

[bobrippling]

This was originally going to just be vim-patch 8.0.1651 (cannot filter :ls output for terminal buffers), however I spotted the last-used feature and decided to include it (patches 7.4.1988 & 8.1.2225).

7.4.1988 - this is a viminfo change, most of which is irrelevant. The patch has just been brought across / mentioned in spirit as it's the commit where I feel the creation and updating b_last_used still belong.

vim-patch:7.4.1988

Problem: When updating viminfo with file marks there is no time order.
Solution: Remember the time when a buffer was last used, store marks for
the most recently used buffers.
vim/vim@ab9c89b

vim-patch:8.0.1651: cannot filter :ls output for terminal buffers

Problem: Cannot filter :ls output for terminal buffers.
Solution: Add flags for terminal buffers. (Marcin Szamotulski, closes vim/vim#2751)
vim/vim@0751f51

vim-patch:8.1.2225: the "last used" info of a buffer is under used

Problem: The "last used" info of a buffer is under used.
Solution: Add "lastused" to getbufinfo(). List buffers sorted by last-used
field. (Andi Massimino, closes vim/vim#4722)
vim/vim@5241057

[teto]

Please prefix the PR with one of WIP/RFC/RDY . Seems like there are a few issues on CI so I guess WIP ? thanks for the PR

[bobrippling]

Knew I'd forgot something! Yes, CI/test failures pending

[bobrippling]

As part of fixing the tests, I either need to have the test wait for more than a second (to give the buffers different timestamps) or add in test_gettime() from vim. I gather that neovim tries to avoid having test_* functions available, are there any opinions on this?

[bobrippling]

I believe the failed tests (functional/terminal/scrollback_spec.lua, functional/ui/spell_spec.lua and functional/api/server_requests_spec.lua) are transient failures - is it possible to requeue those builds?

[janlazo]

@bobrippling test_ functions that do not expose or override internal state are fine. Tests that rely on test_ functions for overriding internal state should be skipped and rewritten to a Lua unit/functional test.