In #36089, `DelegatingReflectionHost` was introduced. Under the hood, it
delegates another `NgccReflectionHost` in order to reflect over the
program's source files, while using a different TypeScript
`ReflectionHost` to reflect over `.d.ts` files (which is how external
dependencies are represented in the program).
Previously, the `NgccReflectionHost`s were used directly in tests. This
does not exercise them in the way they are exercised in the actual
program, because (when used directly) they will also reflect on `.d.ts`
files too (instead of delegating to the TypeScript `ReflectionHost`).
This could hide bugs that would happen on the actual program.
This commit fixes this by using the `DelegatingReflectionHost` in the
various `NgccReflectionHost` tests.
NOTE:
This change will cause some of the existing tests to start failing.
These failures demonstrate pre-existing bugs in ngcc, that were hidden
due to the tests' being inconsistent with how the `ReflectionHost`s are
used in the actual program. They will be fixed in the next commit.
PR Close#36284
93f07aee6c