In the TypeScript compiler API, emit() can be performed either on a single
ts.SourceFile or on the entire ts.Program simultaneously.
ngtsc previously used whole-program emit, which was convenient to use while
spinning up the project but has a significant drawback: it causes a type
checking operation to occur for the whole program, including .d.ts files.
In large Bazel environments (such as Google's codebase), an ngtsc invocation
can have a few .ts files and thousands of .d.ts inputs. This unwanted type
checking is therefore a significant drain on performance.
This commit switches ngtsc to emit each .ts file individually, avoiding the
unwanted type checking.
PR Close#29147
37c5a26421