Problem:  Using wrong window in ll_resize_stack()
          (after v9.1.1287)
Solution: Use "wp" instead of "curwin", even though they are always the
          same value.  Fix typos in documentation (zeertzjq).

closes: vim/vim#17080

https://github.com/vim/vim/commit/b71f1309a210bf8f61a24f4eda336de64c6f0a07

Problem:  quickfix and location-list stack is limited to 10 items
Solution: add the 'chistory' and 'lhistory' options to configure a
          larger quickfix/location list stack
          (64-bitman)

closes: vim/vim#16920

https://github.com/vim/vim/commit/88d41ab270a8390a43da97a903b1a4d76b89d330

Co-authored-by: 64-bitman <60551350+64-bitman@users.noreply.github.com>
Co-authored-by: Hirohito Higashi <h.east.727@gmail.com>

Problem:  inline word diff treats multibyte chars as word char
          (after 9.1.1243)
Solution: treat all non-alphanumeric characters as non-word characters
          (Yee Cheng Chin)

Previously inline word diff simply used Vim's definition of keyword to
determine what is a word, which leads to multi-byte character classes
such as emojis and CJK (Chinese/Japanese/Korean) characters all
classifying as word characters, leading to entire sentences being
grouped as a single word which does not provide meaningful information
in a diff highlight.

Fix this by treating all non-alphanumeric characters (with class number
above 2) as non-word characters, as there is usually no benefit in using
word diff on them. These include CJK characters, emojis, and also
subscript/superscript numbers. Meanwhile, multi-byte characters like
Cyrillic and Greek letters will still continue to considered as words.

Note that this is slightly inconsistent with how words are defined
elsewhere, as Vim usually considers any character with class >=2 to be
a "word".

related: vim/vim#16881 (diff inline highlight)
closes: vim/vim#17050

https://github.com/vim/vim/commit/9aa120f7ada592ed03b37f4de8ee413c5385f123

Co-authored-by: Yee Cheng Chin <ychin.git@gmail.com>

Problem:
First rtp directory is unpredictable and not in line with XDG
base spec.

Solution:
Use stdpath('data')/spell as directory if 'spellfile' is not set.

Co-authored-by: zeertzjq <zeertzjq@outlook.com>
Co-authored-by: Justin M. Keyes <justinkz@gmail.com>

Problem:  cannot set the maximum popup menu width
          (Lucas Mior)
Solution: add the new global option value 'pummaxwidth'
          (glepnir)

fixes: vim/vim#10901
closes: vim/vim#16943

https://github.com/vim/vim/commit/88d75934c3d5bc4c406343f106e1a61638abd3a7

Co-authored-by: glepnir <glephunter@gmail.com>

Problem:  Typos in code and docs related to 'diffopt' "inline:".
          (after v9.1.1243)
Solution: Fix typos and slightly improve the docs.
          (zeertzjq)

closes: vim/vim#16997

https://github.com/vim/vim/commit/5a307c361cbe9f7ac438a917b905378d87f8f2de

Problem:  Diff mode's inline highlighting is lackluster. It only
          performs a line-by-line comparison, and calculates a single
          shortest range within a line that could encompass all the
          changes. In lines with multiple changes, or those that span
          multiple lines, this approach tends to end up highlighting
          much more than necessary.

Solution: Implement new inline highlighting modes by doing per-character
          or per-word diff within the diff block, and highlight only the
          relevant parts, add "inline:simple" to the defaults (which is
          the old behaviour)

This change introduces a new diffopt option "inline:<type>". Setting to
"none" will disable all inline highlighting, "simple" (the default) will
use the old behavior, "char" / "word" will perform a character/word-wise
diff of the texts within each diff block and only highlight the
differences.

The new char/word inline diff only use the internal xdiff, and will
respect diff options such as algorithm choice, icase, and misc iwhite
options. indent-heuristics is always on to perform better sliding.

For character highlight, a post-process of the diff results is first
applied before we show the highlight. This is because a naive diff will
create a result with a lot of small diff chunks and gaps, due to the
repetitive nature of individual characters. The post-process is a
heuristic-based refinement that attempts to merge adjacent diff blocks
if they are separated by a short gap (1-3 characters), and can be
further tuned in the future for better results. This process results in
more characters than necessary being highlighted but overall less visual
noise.

For word highlight, always use first buffer's iskeyword definition.
Otherwise if each buffer has different iskeyword settings we would not
be able to group words properly.

The char/word diffing is always per-diff block, not per line, meaning
that changes that span multiple lines will show up correctly.
Added/removed newlines are not shown by default, but if the user has
'list' set (with "eol" listchar defined), the eol character will be be
highlighted correctly for the specific newline characters.

Also, add a new "DiffTextAdd" highlight group linked to "DiffText" by
default. It allows color schemes to use different colors for texts that
have been added within a line versus modified.

This doesn't interact with linematch perfectly currently. The linematch
feature splits up diff blocks into multiple smaller blocks for better
visual matching, which makes inline highlight less useful especially for
multi-line change (e.g. a line is broken into two lines). This could be
addressed in the future.

As a side change, this also removes the bounds checking introduced to
diff_read() as they were added to mask existing logic bugs that were
properly fixed in vim/vim#16768.

closes: vim/vim#16881

https://github.com/vim/vim/commit/9943d4790e42721a6777da9e12637aa595ba4965

Co-authored-by: Yee Cheng Chin <ychin.git@gmail.com>

Problem:  'completefuzzycollect' does not handle dictionary correctly
Solution: check for ctrl_x_mode_dictionary (glepnir)

closes: vim/vim#16867

https://github.com/vim/vim/commit/587601671cd06ddc4d78f907d98578cdab96003f

Cherry-pick a documentation fix from later.

Co-authored-by: glepnir <glephunter@gmail.com>