'comment_form_fields' filter description should mention the textarea

[SergeyBiryukov]

[35723] introduced the comment_form_fields filter.

Unlike comment_form_default_fields, it includes the textarea, so we should mention it in the filter description.

Something like: "Filter the comment form fields, including the textarea."

[bappi.d.great]

Description updated of comment_form_fields filter

[DrewAPicture]

In 35877:

Docs: Update the summary for the comment_form_fields hook docs to explicitly mention inclusion of the textarea element as a filterable element.

Previously [35723]

Props bappidgreat.
Fixes #34973.