Update modus-themes to version 2.2.0

Update modus-themes to version 2.2.0

* doc/misc/modus-themes.org (Enable and load)
(Differences between loading and enabling): Clarify wording.
(Customization Options): Update sample configuration.
(Option for completion framework aesthetics): Refactor
'modus-themes-completions' to accept an alist value instead of a
symbol.
(Override colors): Elaborate on the example.
(Toggle themes without reloading them): Document sample command that
uses 'enable-theme' instead of 'load-theme'.
(Acknowledgements): Update names of contributors to ideas.
* etc/themes/modus-themes.el (modus-themes-operandi-colors)
(modus-themes-vivendi-colors): Tweak the palette's completion-related
background colors.
(modus-themes-completion-standard-first-match)
(modus-themes-completion-standard-selected)
(modus-themes-completion-extra-selected): Deprecate faces and replace
them with 'modus-themes-completion-selection'.
(modus-themes-completion-key-binding): Rename it to
'modus-themes-key-binding'.
(modus-themes-mode-line): Remove faulty default value.
(modus-themes-completions): Refactor it to accept an alist value.
(modus-themes-box-buttons): Fix typo.
(modus-themes--standard-completions, modus-themes--extra-completions)
(modus-themes--extra-completions-line): Remove outdated private
functions.
(modus-themes--completion): Add new private function.
(modus-themes-faces): Update faces.

* etc/themes/modus-operandi-theme.el:
* etc/themes/modus-vivendi-theme.el: Bump file's version.

For a detailed change log, read:
<https://protesilaos.com/codelog/2022-02-23-modus-themes-2-2-0/>.