Refactor TimeProfiler write methods (NFC)

Refactor TimeProfiler write methods (NFC)

Added a write method for TimeTrace that takes two strings representing
file names. The first is any file name that may have been provided by the
user via `time-trace-file` flag, and the second is a fallback that should
be configured by the caller. This method makes it cleaner to write the
trace output because there is no longer a need to check file names at the
caller and simplifies future TimeTrace usages.

Reviewed By: modocache

Differential Revision: https://reviews.llvm.org/D74514