[flow-isolation] Adopt print/dump pattern for Info and analysis-info dumping
Convert the dump() methods on Info and the FlowIsolation analysis class to
follow the standard Swift C++ compiler pattern: a print(raw_ostream &) method
for the real implementation, with SWIFT_DEBUG_DUMP delegating to it via
llvm::dbgs(). This makes the types consistent with the rest of the codebase and
allows callers to redirect output to arbitrary streams.