[Backport release-0.8] doc (#20616)

docs: various

- increase python line-length limit from 88 => 100.
- gen_help_html: fix bug in "tag" case (tbl_count => tbl_contains)

ref #15632
fix #18215
fix #18479
fix #20527
fix #20532

Co-authored-by: Ben Weedon <ben@weedon.email>
(cherry picked from commit f37cd2bb15)

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

src/nvim/api/buffer.c

@@ -355,6 +355,8 @@ static bool check_string_array(Array arr, bool disallow_nl, Error *err)
 /// Out-of-bounds indices are clamped to the nearest valid value, unless
 /// `strict_indexing` is set.
 ///
+/// @see |nvim_buf_set_text()|
+///
 /// @param channel_id
 /// @param buffer           Buffer handle, or 0 for current buffer
 /// @param start            First line index
@@ -527,6 +529,8 @@ end:
 ///
 /// Prefer |nvim_buf_set_lines()| if you are only adding or deleting entire lines.
 ///
+/// @see |nvim_buf_set_lines()|
+///
 /// @param channel_id
 /// @param buffer           Buffer handle, or 0 for current buffer
 /// @param start_row        First line index