When multiple occurrences of the same package exist within a single
TypeScript compilation unit, TypeScript deduplicates the source files
by introducing redirected source file proxies. Such proxies are
recreated during an incremental compilation even if the original
declaration file did not change, which caused the compiler not to reuse
any work from the prior compilation.
This commit changes the incremental driver to recognize a redirected
source file and treat them as their unredirected source file.
PR Close#41448