MDL-83634 tool_brickfield: Downgrade image alt text check's severity

Given that
* There is no formally defined limit for alt text length,
* Current versions of screen readers can read alt texts longer than
125 characters,
* Accessibility checkers like axe DevTools, WAVE, etc., do not raise
errors or warnings about long image alt texts.

This patch:
- Downgrades the default severity for the `img_alt_is_too_long`
check from `BA_TEST_SEVERE` to `BA_TEST_SUGGESTION`.
- Updates the `checkdesc:imgaltistoolong` lang string to be more of a
reminder/suggestion rather than an error.

admin/tool/brickfield/classes/local/htmlchecker/common/checks/img_alt_is_too_long.php

@@ -30,10 +30,6 @@ use tool_brickfield\local\htmlchecker\common\brickfield_accessibility_test;
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 class img_alt_is_too_long extends brickfield_accessibility_test {
-
-    /** @var int The default severity code for this test. */
-    public $defaultseverity = \tool_brickfield\local\htmlchecker\brickfield_accessibility::BA_TEST_SEVERE;
-
     /**
      * The main check function. This is called by the parent class to actually check content.
      */

admin/tool/brickfield/lang/en/tool_brickfield.php

@@ -179,7 +179,7 @@ $string['checkdesc:headerh3'] = 'Headers following after H3 headers (the editor
 $string['checkdesc:headershavetext'] = 'A header needs to contain text to be perceivable.';
 $string['checkdesc:iisnotused'] = 'Italic (i) elements should not be used; "em" should be used instead.';
 $string['checkdesc:imgaltisdifferent'] = 'Image alt (alternative) text should not be the image filename.';
-$string['checkdesc:imgaltistoolong'] = 'Image alt (alternative) text should not be more than the maximum allowed (125) characters.';
+$string['checkdesc:imgaltistoolong'] = 'Ensure that the image alt (alternative) text is concise enough to describe the image.';
 $string['checkdesc:imgaltnotemptyinanchor'] = 'Image alt (alternative) text should not be empty, especially when the image has a link going elsewhere.';
 $string['checkdesc:imgaltnotplaceholder'] = 'Image alt (alternative) text should not be a simple placeholder text, such as "image".';
 $string['checkdesc:imghasalt'] = 'Image alt (alternative) text should not be missing for image elements, unless purely decorative with no meaning.';