Update runtime files
https://github.com/vim/vim/commit/d2ea7cf10a4d026ebd402594d656af7d5c811c24

omit `runtime/doc/if_tcl.txt`
omit `runtime/doc/textprop.txt`
omit `runtime/tutor/*`
omit `runtime/syntax/vim.vim` (cherry-picked in https://github.com/neovim/neovim/commit/2dd7828511d04a8b7f1ac4331c719a751a5db869)

manual merge of `runtime/pack/dist/opt/termdebug/plugin/termdebug.vim`

Problem:    More functions can be used as a method.
Solution:   Add has_key(), split(), str2list(), etc.
https://github.com/vim/vim/commit/a74e4946de074d2916e3d6004f7fa1810d12dda9

Problem:    Using "syn include" does not work properly.
Solution:   Don't add current_syn_inc_tag to topgrp. (Jaehwang Jerry Jung,
            closes vim/vim#8104)
https://github.com/vim/vim/commit/2e240bd428c0033d16f201d7f837636412358199

Cherry-pick AssertHighlightGroups from patch v8.2.2068.

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:    "syn sync" reports a very large number.
Solution:   Use "at the first line".
https://github.com/vim/vim/commit/9950280d377a5c0706d141017fcef9cad598b8b0

Problem:    No syntax HL after splitting windows with :bufdo. (Yasuhiro
            Matsumoto)
Solution:   Trigger Syntax autocommands in buffers that are active.
            (closes vim/vim#4761)
https://github.com/vim/vim/commit/c7f1e4002184903f4e12e429dd5c6ab731932f86

Problem:    Crash when using ":set" after ":ownsyntax".
Solution:   Make sure 'spelloptions' is not NULL. (closes vim/vim#6950)
https://github.com/vim/vim/commit/d1f76afaf963be706697279ab0570ffcb8a1f2fc

Problem:    Syntax foldlevel is taken from the start of the line.
Solution:   Add ":syn foldlevel" to be able to use the minimal foldlevel in the line.
https://github.com/vim/vim/commit/e35a52aee718c881bdfa69a47a1068df6ab6c60a

With `foldmethod=syntax` the foldlevel of a line is computed based
on syntax items on the line.  Previously we always used the level
of the syntax item containing the start of the line.  This works
well in cases such as:

    if (...) {
      ...
    }
    else if (...) {
      ...
    }
    else {
      ...
    }

which folds like this:

    +---  3 lines: if (...) {---------------------------
    +---  3 lines: else if (...) {----------------------
    +---  3 lines: else {-------------------------------

However, the code:

    if (...) {
      ...
    } else if (...) {
      ...
    } else {
      ...
    }

folds like this:

    +---  7 lines: if (...) {---------------------------

We can make the latter case fold like this:

    +---  2 lines: if (...) {---------------------------
    +---  2 lines: } else if (...) {--------------------
    +---  3 lines: } else {-----------------------------

by choosing on each line the lowest fold level that is followed
by a higher fold level.

Add a syntax command

    :syntax foldlevel [start | minimum]

to choose between these two methods of computing the foldlevel of
a line.

Problem:    Syntax test fails on Mac.
Solution:   Limit the window size to 20 rows.
https://github.com/vim/vim/commit/83e9a1ce75818a78c5ddf8dcfb820634ca6fabff

Problem:    Syntax test fails.
Solution:   Add missing file patch.
https://github.com/vim/vim/commit/bbfd1562aeaa5b40b6451effc399846b692d6992