Rename factory functions from 'Create' to 'Make' (#3706)

Similar to #3705, we actually have a mix of `Make` and `Create` in
factory functions too, so this PR is normalizing on `Make`. It's
intended to be consistent with the naming choice for Carbon factory
functions.

Note, MakeSyntheticBlock is the only one I feel a little weird about
because llvm's own APIs use Create, and this is essentially wrapping
LLVM calls. But the flipside is it also feels like a vague line to draw,
when we also differ from LLVM coding style in other ways.

toolchain/lex/tokenized_buffer_benchmark.cpp

@@ -396,8 +396,8 @@ 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_, filename_, ConsoleDiagnosticConsumer()));
+    return std::move(*SourceBuffer::MakeFromFile(fs_, filename_,
+                                                 ConsoleDiagnosticConsumer()));
   }
 
   SharedValueStores value_stores_;