Create 1P testing utilities for Angular

Need a way to ergonomically set props on components during unit tests. This should be part of a testing public API

Something like
```
setProps(componentInstance, {
prop1: 'foo',
prop2: 42,
})
```

and setProps would take care of providing a type safe signature, also create the BoundProperty objects.

Look for existing testing utilities in the codebase, likely under a directory like `testing/` or `src/testing/`. Understand how components are currently tested and how BoundProperty objects are created. The goal is to design and implement a `setProps` function that integrates with Angular's testing APIs and provides type safety.

索引モデルが issue の本文から書いたものです。