In the compiler, the `NgtscProgram` is responsible for creating the
`ts.Program` instance to use, potentially using a `ts.Program` from a
prior compilation to enable incremental compilation. It used to track
a `reuseTsProgram` for this purpose, however the `ts.Program` that
should be used as reuse program is also tracked by the `NgCompiler`
instance that is used by `NgtscProgram`. The `NgtscProgram` can leverage
the state from `NgCompiler` instead of keeping track of it by itself.
PR Close#41289