incorrect description for $editor_id param to wp_editor()

[pbiron]

The description for $editor_id says:

HTML ID attribute value for the textarea and TinyMCE. Can only be /[a-z]+/.

While $editor_id can't contain a [ character (introduced in [27950], which does a _deprecated_argument() call), as far as I can tell, there are no other restrictions on $editor_id as long as it is a legal value for an HTML @id.

Additionally, wp_editor() passes $editor_id on to _WP_Editors::editor(), and the description for $editor_id param for that method specifies a different restriction on the legal values for it:

ID for the textarea and TinyMCE and Quicktags instances (can contain only ASCII letters and numbers).

[SergeyBiryukov]

Related: [18498], [19239], [32899].

[SergeyBiryukov]

It's worth noting that [32899] introduced $editor_id_attr = esc_attr( $editor_id ), so the restrictions seem less relevant now, apart from the [] brackets limitation.

[SergeyBiryukov]

In 47210:

Docs: Improve description for the $editor_id parameter of wp_editor() and _WP_Editors::editor().

The restictions mentioned for the parameter value should be consistenct.

Props pbiron, SergeyBiryukov.
Fixes #49384.