Various improvements to font-lock-settings for elixir-ts-mode

Various improvements to font-lock-settings for elixir-ts-mode

Changes and made from conversations from the Elixir slack channel,
the github issue
https://github.com/wkirschbaum/elixir-ts-mode/issues/35 and bug#67246.

* lisp/progmodes/elixir-ts-mode.el
(elixir-ts--font-lock-settings): Update features.
(elixir-ts-mode): Update treesit-font-lock-feature-list.
(elixir-ts-font-comment-doc-identifier-face): Rename to
elixir-ts-comment-doc-identifier.
(elixir-ts-font-comment-doc-attribute-face): Rename to
elixir-ts-comment-doc-attribute.
(elixir-ts-font-sigil-name-face): Rename to elixir-ts-sigil-name.
(elixir-ts-atom-key-face)
(elixir-ts-keyword-key-face)
(elixir-ts-attribute-face): Add new custom face.