feat: Add support for flyout menu mode in MegaMenu

- Introduced `MegaMenuMode` type and `normalizeMegaMenuMode` function to handle menu modes.
- Updated `MegaMenuApplicationCustomizer` to accept `menuMode` property.
- Enhanced `MegaMenuRenderer` to render flyout menus based on the selected mode.
- Created new HTML previews for both flyout and mega menu modes.
- Removed unused mock services and user custom action service interfaces.

gulpfile.js

@@ -3,5 +3,6 @@
 const build = require('@microsoft/sp-build-web');
 
 build.addSuppression(`Warning - [sass] The local CSS class 'ms-Grid' is not camelCase and will not be type-safe.`);
+build.addSuppression(`Warning - MegaMenuApplicationCustomizer: Admins can make this solution available to all sites in the organization, but extensions won’t automatically appear. SharePoint Framework extensions must be specifically associated to sites, lists, and fields programmatically to be visible to site users.`);
 
-build.initialize(require('gulp'));
+build.initialize(require('gulp'));