Add bottom-nav entry point to v21.0.0 migration

Added mappings for all bottom-nav exports to the ENTRY_POINT_MAP:
- IgxBottomNavComponent
- IgxBottomNavModule
- IgxBottomNavItemComponent
- IgxBottomNavHeaderComponent
- IgxBottomNavContentComponent
- IgxBottomNavHeaderLabelDirective
- IgxBottomNavHeaderIconDirective
- IGX_BOTTOM_NAV_DIRECTIVES

The migration will now automatically migrate bottom-nav imports from 'igniteui-angular' to 'igniteui-angular/bottom-nav' when users opt-in during ng update.

Co-authored-by: kdinev <[email protected]>

Author: Copilot

projects/igniteui-angular/migrations/update-21_0_0/index.ts

@@ -107,6 +107,16 @@ const ENTRY_POINT_MAP = new Map<string, string>([
     ['IBannerEventArgs', 'banner'],
     ['IBannerCancelEventArgs', 'banner'],
 
+    // Bottom Nav
+    ['IgxBottomNavComponent', 'bottom-nav'],
+    ['IgxBottomNavModule', 'bottom-nav'],
+    ['IgxBottomNavItemComponent', 'bottom-nav'],
+    ['IgxBottomNavHeaderComponent', 'bottom-nav'],
+    ['IgxBottomNavContentComponent', 'bottom-nav'],
+    ['IgxBottomNavHeaderLabelDirective', 'bottom-nav'],
+    ['IgxBottomNavHeaderIconDirective', 'bottom-nav'],
+    ['IGX_BOTTOM_NAV_DIRECTIVES', 'bottom-nav'],
+    
     // Button Group
     ['IgxButtonGroupComponent', 'buttonGroup'],
     ['IgxButtonGroupModule', 'buttonGroup'],