Switch SourceBuffer to diagnostics. (#3197)

This updates SourceBuffer to diagnostics. Some additional edits to
diagnostics were necessary due to issues moving arguments around, which
seems to stem from a compile error with clang 14 (fixed in later
versions).

---------

Co-authored-by: Richard Smith <richard@metafoo.co.uk>

toolchain/lex/tokenized_buffer_benchmark.cpp

@@ -10,6 +10,7 @@
 #include "common/check.h"
 #include "llvm/ADT/Sequence.h"
 #include "llvm/ADT/StringExtras.h"
+#include "toolchain/diagnostics/diagnostic_emitter.h"
 #include "toolchain/diagnostics/null_diagnostics.h"
 #include "toolchain/lex/token_kind.h"
 #include "toolchain/lex/tokenized_buffer.h"
@@ -297,8 +298,8 @@ class LexerBenchHelper {
   auto MakeSourceBuffer(llvm::StringRef text) -> SourceBuffer {
     CARBON_CHECK(fs_.addFile(filename_, /*ModificationTime=*/0,
                              llvm::MemoryBuffer::getMemBuffer(text)));
-    return std::move(
-        *SourceBuffer::CreateFromFile(fs_, llvm::errs(), filename_));
+    return std::move(*SourceBuffer::CreateFromFile(
+        fs_, filename_, ConsoleDiagnosticConsumer()));
   }
 
   llvm::vfs::InMemoryFileSystem fs_;