Remove 128-character limit on image captions and descriptions

Problem/Motivation

Custom captions and descriptions in the GLightbox image and responsive-image formatters are limited to 128 characters by Drupal's textfield default. This is too short for captions combining several tokens.

Steps to reproduce

1. Open the settings for an image field using the GLightbox or GLightbox Responsive formatter.
2. Select Custom (with tokens) for Caption or Caption description.
3. Try to enter text or a token pattern longer than 128 characters.

Proposed resolution

Use textareas for both settings in both formatters. Stored values remain strings.

The equivalent remote-video proposal is #3628605.

Local testing

With the locally prepared change, browser checks on Drupal 11.4.8 confirm both inputs retain 740 characters in display and Views-style forms, for both formatters.

Remaining tasks

Review the MR (verify saving, reopening and rendering longer captions and descriptions) then merge MR.