Problem:
Subdirectories like "visual", "insert", "normal" encourage people to
separate *related* tests for no good reason.  Typically the _mode_ is
not the relevant topic of a test (and when it is, _then_ create
an appropriate describe() or it()).

Solution:
- Delete the various `test/functional/<mode>/` subdirectories, move
  their tests to more meaningful topics.
- Rename `…/normal/` to `…/editor/`.
  - Move or merge `…/visual/*` and `…/insert/*` tests into here where
    appropriate.
- Rename `…/eval/` to `…/vimscript/`.
  - Move `…/viml/*` into here also.

* test(reorg): insert/* => editor/mode_insert_spec.lua
* test(reorg): cmdline/* => editor/mode_cmdline_spec.lua
* test(reorg): eval core tests => eval_spec.lua

Problem:    Cannot handle binary data.
Solution:   Add the Blob type. (Yasuhiro Matsumoto, closes vim/vim#3638)
https://github.com/vim/vim/commit/6e5ea8d2a995b32bbc5972edc4f827b959f2702f

Nvim-specific Blob conversions are implemented in future commits.

Refactor write_blob() to use a FileDescriptor, as f_writefile() was
refactored to use one (does not apply to read_blob()).

Use var_check_lock() in f_add() for Blobs from v8.1.0897.

Add a modeline to test_blob.vim and fix some doc typos.

Include if_perl.txt's VIM::Blob() documentation. Interestingly, this
function already worked before this port, as it just returns a Blob
string literal, not an actual Blob object.

N/A patches for version.c:

vim-patch:8.1.0741: viminfo with Blob is not tested

Problem:    Viminfo with Blob is not tested.
Solution:   Extend the viminfo test.  Fix reading a blob.  Fixed storing a
            special variable value.
https://github.com/vim/vim/commit/8c8b8bb56c724cc1bfc3d8520eec33f2d399697c

vim-patch:8.1.1022: may use NULL pointer when out of memory

Problem:    May use NULL pointer when out of memory. (Coverity)
Solution:   Check for blob_alloc() returning NULL.
https://github.com/vim/vim/commit/e142a9467a7f6845a426d8db6efedf246d3c13ac

v8.1.0736 made some changes for making some emsgs more specific.
Includes the change for Test_lambda_fails() in test_lambda.vim.
Adjust relevant functionaltests to expect the new emsgs.

This patch has been fully ported in my Blob port PR, but it hasn't been
merged yet, so just use what we need from it for now.

Required for v8.1.1821.

Problem:    Cannot use "q" to cancel a number prompt.
Solution:   Recognize "q" instead of ignoring it.
https://github.com/vim/vim/commit/eebd555733491cb55b9f30fe28772c0fd0ebacf7

Problem:    Line() only works for the current window.
Solution:   Add an optional argument for the window to use.
https://github.com/vim/vim/commit/8e0a8e7eb7c177807f44db6b76d8e52314248ab5

Replacement for Vim's test_null_string().
Vim uses it to verify that its codebase handles null strings.
Preparation for the Test_null_list() in patch v8.2.1822.

Use v:_null_string, not non-existent env var, for null string tests.

Mention v:_null_string in id() because id(v:_null_string) returns (nil).

This reverts commit 0519a75f6eca1065a4d0184f99c71ae03a99b9b1.

Problem:    Peeking and flushing output slows down execution.
Solution:   Do not update the mode message when global_busy is set.  Do not
            flush when only peeking for a character. (Ken Takata)
https://github.com/vim/vim/commit/cb574f415486adff645ce384979bfecf27f5be8c

Problem:    List/dict test fails.
Solution:   Correct expected exception.
https://github.com/vim/vim/commit/6d967125ad87b1c2a9467357286c3514d5dd1c40

Cherry-pick e_dictkey[] change from patch 8.2.1924.

N/A patches for version.c:

vim-patch:8.2.1929: MS-Windows: problem loading Perl 5.32

Problem:    MS-Windows: problem loading Perl 5.32.
Solution:   Define NO_THREAD_SAFE_LOCALE. (Ken Takata, closes vim/vim#7234)
https://github.com/vim/vim/commit/0289065e41ce3148f929e16a55aa3b161c80576f

vim-patch:8.2.1932: compiler warnings when building with Athena GUI

Problem:    Compiler warnings when building with Athena GUI.
Solution:   Fix function signatures.
https://github.com/vim/vim/commit/963734e316bd17dd7290abcac28b875435d06381