LearnDash LMS 4.21.1

* Fix - Resolved issue where standalone quizzes did not trigger the learndash_quiz_completed action.
* Fix - Resolved issue where the LearnDash Customizer outputted the default CSS values, changing the CSS priorities and affecting some themes.
* Fix - Resolved issue where the switch field in admin settings was not displaying the label correctly depending on the state.
* Tweak - Deprecated constants: LEARNDASH_QUIZ_ESSAY_SUBMIT_COMPLETED.
* Tweak - Updated templates: `modules/ai/virtual-instructor/message-default.php`, `modules/ai/virtual-instructor/message-error.php`.

* Feature - Customizer settings for the LearnDash 3.0 template.
* Fix - Fixed issue where adding directory index file causes PHP notices when the directory is not writable.
* Fix - Resolved issue where admins cannot disable all toggles in certain metaboxes.
* Fix - Resolved issue where Additional Question Options won't stay toggled on when only "Randomize Answers" is enabled.
* Fix - Resolved issue where Windows-based servers were unable to use the Import tool.
* Fix - Resolved issue where adding a percentage symbol in password in login form would change the password.
* Fix - Resolved issue where TrustedLogin access link doesn't auto log in the user.
* Tweak - Updated functions: `learndash_put_directory_index_file`.
* Tweak - Added filters: `learndash_customizer_config`, `learndash_customizer_control`, `learndash_customizer_css_priority`, `learndash_customizer_themes`.
* Tweak - Added actions: `learndash_customizer_control_add_after`, `learndash_customizer_control_add_before`, `learndash_customizer_panel_add_after`, `learndash_customizer_panel_add_before`, `learndash_customizer_section_add_after`, `learndash_customizer_section_add_before`, `learndash_customizer_setting_add_after`, `learndash_customizer_setting_add_before`, `learndash_customizer_themes_init_after`, `learndash_customizer_themes_init_before`, `learndash_customizer_theme_init_after`, `learndash_customizer_theme_init_before`.

* Feature - Added decimal and negative number support to quiz points.
* Feature - Added "Different points for each answer" option support to the quiz builder.
* Fix - Resolved issue where NaN points label could appear if points were deleted in the quiz builder.
* Fix - Fixed quiz statistics loading for quizzes where all questions are set to 0 points.
* Fix - Improved question and answer points synchronization in the quiz builder.
* Fix - Resolved issue where the question settings were ignored in the quiz builder when the existing question was added.
* Fix - Resolved issue where the question was being duplicated on deletion in the quiz builder sidebar in some cases.
* Fix - Resolved issue where the free choice question points are calculated incorrectly when the different points mode is enabled.
* Tweak - Added points calculation within the POST route in the `ldlms/v1/sfwd-questions/<id>` REST API endpoint.
* Tweak - Updated constants: WPPROQUIZ_VERSION.
* Tweak - Updated functions: `learndash_format_course_points`, `learndash_get_essay_details`, `learndash_proquiz_sync_question_fields`, `learndash_question_assessment_fetch_data`, `learndash_question_cloze_fetch_data`, `learndash_question_free_get_answer_data`, `learndash_update_quiz_statistics`.
* Tweak - Updated filters: `learndash_course_points_format_round`, `learndash_fetch_quiz_questions`, `learndash_ques_free_answer_pts`, `learndash_ques_multiple_answer_pts_each`, `learndash_ques_multiple_answer_pts_whole`, `learndash_ques_single_answer_pts`, `learndash_quiz_question_answer_preprocess`.
* Tweak - Updated templates: `legacy/templates/quiz/partials/show_quiz_questions_box.php`.