[Remarks] Add a specialized RemarkStreamer for SIL remarks

This allows the usage of the whole remark infrastructure developed in
LLVM, which includes a new binary format, metadata in object files, etc.

This gets rid of the YAMLTraits-based remark serialization and does the
plumbing for hooking to LLVM's main remark streamer.

For more about the idea behind LLVM's main remark streamer, see the
docs/Remarks.rst changes in https://reviews.llvm.org/D73676.

The flags are now:

* -save-optimization-record: enable remarks, defaults to YAML
* -save-optimization-record=<format>: enable remarks, use <format> for
serialization
* -save-optimization-record-passes <regex>: only serialize passes that
match <regex>.

The YAMLTraits in swift had a different `flow` setting for the debug
location, resulting in some test changes.

include/swift/Driver/ToolChain.h

@@ -317,6 +317,9 @@ public:
   virtual void validateArguments(DiagnosticEngine &diags,
                                  const llvm::opt::ArgList &args,
                                  StringRef defaultTarget) const {}
+
+  llvm::Expected<file_types::ID>
+  remarkFileTypeFromArgs(const llvm::opt::ArgList &Args) const;
 };
 } // end namespace driver
 } // end namespace swift