[6.x] User Groups create / edit

[brianjhanson]

Building on #18686 this brings the Create & Edit user groups page into Inertia

New Components and UI Enhancements:

• Added PermissionList.vue for displaying and managing nested permissions with checkbox indentation and group selection/deselection logic. This paged doesn't use our craft-checkbox-indeterminate component intentionally as the logic we want to use on this page is a little different than that component is designed for. Maybe some day in the future we could use it, but that day is not today.
• Introduced InlineFlash.vue to show inline success or error messages using a new useFlash composable for flash message handling. [1] [2]
• Added ErrorSummary.vue to display a summary of form errors in a callout above the form content.

User Group Settings Page Improvements:

• Refactored SettingsUserGroupsEditPage.vue to use the new AppLayout form API, integrate permission management with PermissionList, and handle group actions (such as delete) and keyboard shortcuts for saving.
• Updated SettingsUserGroupsIndexPage.vue to use the shared UserGroup type and improved table column configuration. [1] [2] [3]

Form Handling and Layout Updates:

• Enhanced AppLayout.vue to support form submission, display error summaries, show inline flash messages, and provide a more flexible actions slot with support for custom and default actions (including an action menu for save options). [1] [2] [3]

Component and Styling Improvements:

• Updated CraftCheckbox to support a customizable horizontal gap and new sizing token for improved alignment and consistency. [1] [2] [3]
• Improved the Vue wrapper generator to support error feedback in component props and templates.
• Enhanced ActionMenu.vue to support custom invoker slots and display keyboard shortcuts for actions. [1] [2] [3] [4]