The `NgccReflectionHost`s have logic for detecting certain known
declarations (such as `Object.assign()` and TypeScript helpers), which
allows the `PartialEvaluator` to evaluate expressions it would not be
able to statically evaluate otherwise.
This commit moves the logic for identifying these known declarations to
dedicated methods. This is in preparation of allowing ngcc's
`DelegatingReflectionHost` (introduced in #36089) to also apply the
known declaration detection logic when reflecting on TypeScript sources.
PR Close#36284
0af6e9fcbb