feat(@schematics/angular): add migrate-karma-to-vitest update migration

Migrate projects using the Karma unit-test builder to the new
@angular/build:unit-test builder with Vitest.

This migration automatically updates target builders, translates builder options
(such as coverage and browsers format), moves custom build options to dedicated
configurations to prevent loss of custom settings, cleans up default
configuration files, and installs required Vitest runner packages.

Author: clydin