This is a port of these two patches combined:

vim-patch:8.1.1524: tests are silently skipped

Problem:    Tests are silently skipped.
Solution:   Throw an exception for skipped tests in more places.
https://github.com/vim/vim/commit/b0f94c1ff34d27d33aa9f96204985ea29c2eb0a1

vim-patch:8.1.1544: some balloon tests don't run when they can

Problem:    Some balloon tests don't run when they can.
Solution:   Split GUI balloon tests off into a separate file. (Ozaki Kiichi,
            closes vim/vim#4538)  Change the feature check into a command for
            consistency.
https://github.com/vim/vim/commit/b46fecd3454399f8ebdc5055302e4bfc5a10f98b

Omit test_lua.vim: previous patches are N/A
Omit test_memory_usage.vim: previous patches are N/A
Omit test_textprop.vim: previous patches are N/A
Omit test_winbar.vim: previous patches are N/A
Omit test_termcodes.vim: mostly N/A
Skip Test_mouse_positon() because it uses test_setmouse().
Cannot throw error in a Test_nocatch_ test.
Use latest `CheckFeature clipboard_working` for test_quotestar.vim

Problem:    Command line completion not fully tested.
Solution:   Add more test cases.  Make help sorting stable. (Dominique Pelle,
            closes vim/vim#5402)
https://github.com/vim/vim/commit/297610ba4b110c918ffe60c45eb4a1d6ea2daae5

Problem:    search() gets stuck with "c" and skip evaluates to true.
Solution:   Reset the SEARCH_START option. (closes vim/vim#10608)
https://github.com/vim/vim/commit/180246cfd1a5842c538fa8a4a0b520f1d95c90c7

Problem:    Transparent syntax item uses start/end of containing region.
Solution:   Do not change the startpos and endpos of a transparent region to
            that of its containing region. (Adrian Ghizaru, closes vim/vim#7349,
            closes vim/vim#7391)
https://github.com/vim/vim/commit/b46f57e87b3706a8c4b97d8e03f7853a7938b061

Problem:    Using freed memory when using synstack() and synID() in WinEnter.
Solution:   Check using the syntax window. (closes vim/vim#10204)
https://github.com/vim/vim/commit/ca7e86c23789eb0ed8f6400f25ea9e0e1036f9fc

Problem:    Search() cannot skip over matches like searchpair() can.
Solution:   Add an optional "skip" argument. (Christian Brabandt, closes vim/vim#861)
https://github.com/vim/vim/commit/adc17a5f9d207fd1623fd923457a46efc9214777

Enable skip arg usage in autoload/freebasic.vim

evalarg_T doesn't really matter because it's deleted in v8.2.0918 (and
reincarnated for Vim9 script in v8.2.1047), but I found out too late :P Anyway:

- Port evalarg_T into eval.h and use const char * and Callback fields
- Use EVALARG_INIT to initialize
- Return bool over OK/FAIL from evalarg functions
- Remove check from evalarg_clean as callback_free ignores None callbacks anyway
- Move eva_buf field into evalarg_get as a local (not sure what reason it has
  being in the struct)

N/A patches for version.c:

vim-patch:8.2.4355: unnecessary call to check_colorcolumn()

Problem:    Unnecessary call to check_colorcolumn().
Solution:   Remove the call. (Sean Dewar, closes vim/vim#9748)
https://github.com/vim/vim/commit/0f7ff851cb721bb3c07261adbf82b591229f530d

We should now be equal with Vim in regards to method call support of already ported built-ins.

Enable all relevant commented-out uses of the syntax in tests that I could grep.

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.