[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>

runtime/lua/vim/_editor.lua

@@ -12,21 +12,8 @@
 -- Guideline: "If in doubt, put it in the runtime".
 --
 -- Most functions should live directly in `vim.`, not in submodules.
--- The only "forbidden" names are those claimed by legacy `if_lua`:
---    $ vim
---    :lua for k,v in pairs(vim) do print(k) end
---    buffer
---    open
---    window
---    lastline
---    firstline
---    type
---    line
---    eval
---    dict
---    beep
---    list
---    command
+--
+-- Compatibility with Vim's `if_lua` is explicitly a non-goal.
 --
 -- Reference (#6580):
 --    - https://github.com/luafun/luafun
@@ -122,9 +109,7 @@ function vim._os_proc_children(ppid)
   return children
 end
 
--- TODO(ZyX-I): Create compatibility layer.
-
---- Return a human-readable representation of the given object.
+--- Gets a human-readable representation of the given object.
 ---
 ---@see https://github.com/kikito/inspect.lua
 ---@see https://github.com/mpeterv/vinspect