Problem:
The generated ToC (table of contents) uses anchors derived from the
heading title, e.g. the "Global Plugins" heading yields:
https://neovim.io/doc/user/usr_05.html#_global-plugins-
so if the heading title changes, then the old URL (anchor) is broken.

Solution:
:help tags change less often than heading titles, so if a heading
contains a *tag*, use that as its anchor name instead. Example:
https://neovim.io/doc/user/usr_05.html#standard-plugin

- Improve generated HTML by updating parser which includes fixes for
  single "'" and single "|":
  https://github.com/neovim/tree-sitter-vimdoc/pull/31
- Updated parser also fixes the conceal issue for "help" highlight
  queries https://github.com/neovim/tree-sitter-vimdoc/issues/23 by
  NOT including whitespace in nodes.
  - But this means we need to restore the getws() function which scrapes
    leading whitespace from the original input (buffer).

- 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>