Problem:    Some Normal mode commands not fully tested.
Solution:   Add a few more tests. (Yegappan Lakshmanan, closes vim/vim#7073)
https://github.com/vim/vim/commit/d1ad99b65470d3e754f6a0588a6b0dc2214a1eab

Cherry-pick test_registers.vim change from patch 8.2.0644.

Problem:    Ex command error cannot contain an argument.
Solution:   Add ex_errmsg() and translate earlier.  Use e_trailing_arg where
            possible.
https://github.com/vim/vim/commit/8930caaa1a283092aca81fdbc3fcf15c7eadb197

Remove duplicate test file 062_tab_pages_spec.lua

Problem:    Insufficient testing for src/window.c.
Solution:   Add more tests. (Yegappan Lakshmanan, closes vim/vim#6345)
https://github.com/vim/vim/commit/5d3c9f8c2a0fc29ba4ac8e0f052378b64d9e3dd3

Cherry-pick test_tagjump.vim changes from patch 8.1.2373.

Problem:    Some code not covered by tests.
Solution:   Add test cases. (Yegappan Lakshmanan, closes vim/vim#5649)
https://github.com/vim/vim/commit/bc2b71d44a0b90b6aeb3534a76912fccbe5577df

Problem:    Previous tab page not usable from an Ex command.
Solution:   Add the "#" argument for :tabnext et al. (Yegappan Lakshmanan,
            closes vim/vim#6677)
https://github.com/vim/vim/commit/94f4ffa7704921a3634e56b878e6dc362bc3d508

Do not rename old_curtab to prev_tp in win_new_tabpage, this can be confused
with the previous tabpage (`:tabprevious`).

Cherry-pick ex_errmsg from v8.2.1280.
https://github.com/vim/vim/commit/8930caaa1a283092aca81fdbc3fcf15c7eadb197

Problem:    Cannot jump to the last used tabpage.
Solution:   Add g<Tab> and tabpagnr('#'). (Yegappan Lakshmanan, closes vim/vim#6661,
            neovim #11626)
https://github.com/vim/vim/commit/62a232506d06f6d1b3b7271801c907d6294dfe84

Nvim implemented this feature before Vim, but Vim made some useful changes (e.g:
beeping on failure). Port the changes to closer match Vim (also makes porting
future patches easier).

Also note that because CHECK_CMDWIN was added to goto_tabpage_tp, there is no
need to do the extra work with tabpage_index and goto_tabpage inside
goto_tabpage_lastused to fix cmdwin issues any more (#11692).
Note that while goto_tabpage_tp doesn't check for textlock like goto_tabpage
does, it shouldn't matter as it is already checked for earlier.

Add tags for <C-Tab> to tabpage.txt, and refer to <C-Tab> over CTRL-Tab to be
consistent with other docs like the patch.
Remove mention of "previous tabpage" (it can be confused with the tabpage to the
left, e.g: `:tabprevious`).
Similarly, don't rename old_curtab to last_tab in enter_tabpage (it might be
confused with the right-most tabpage, e.g: `:tablast`).

Cherry-pick Test_tabpage change from v8.2.0634.
https://github.com/vim/vim/commit/92b83ccfda7a1d654ccaaf161a9c8a8e01fbcf76

Problem:    More functions can be used as methods.
Solution:   Make various functions usable as a method.
https://github.com/vim/vim/commit/aad222c9c9a1e4fe6ae5a1fe95bb084619be0e65

Partial port as this does not include eval.txt change for listener_add.

Cherry-pick eval.txt changes for:
- bufadd from v8.1.1626:
  https://github.com/vim/vim/commit/5ca1ac373ae62b37152cb6f85916b402eda520a5
- setloclist and setqflist headers from:
  https://github.com/vim/vim/commit/b0d45e7f5354375edd02afafde3bd37dac1515ff

Correct eval.txt typo for settabwinvar method call (matches latest Vim).

Problem:    Typos and small problems in test files.
Solution:   Small improvements.
https://github.com/vim/vim/commit/037c54f261818439755d56e318da068f97997fb5

Include unmerged patch v8.0.1200 changes
because this patch depends on `set beloff=all` removed in 1 test.

Problem:    Tabpage menu and tabline not sufficiently tested.
Solution:   Add tests. (Yegappan Lakshmanan, closes vim/vim#6307)
https://github.com/vim/vim/commit/8c524f76ebd43f006e765534765b595de7095f12

Cherry-pick Test_entering_digraph() from patch v8.2.1022.
Cherry-pick :CheckGui from patch v8.1.1826.

Problem:    BufEnter autocmd not triggered on ":tab drop". (Andy Stewart)
Solution:   Decrement autocmd_no_enter for the last file. (closes vim/vim#1660,
            closes vim/vim#5473)
https://github.com/vim/vim/commit/c10b521628f2b073fa231defa26f23937c91724d

N/A patches for version.c:

vim-patch:8.1.1805: au_did_filetype is declared twice

Problem:    Au_did_filetype is declared twice.
Solution:   Remove it from autocmd.c. (closes vim/vim#4767)
https://github.com/vim/vim/commit/6cd57d44669c02af9195f5601b882edd435b47e8