Switch Driver back to parameters for construction (#4849)

This is for more complex construction, see #4846

toolchain/check/check_fuzzer.cpp

@@ -39,12 +39,8 @@ extern "C" int LLVMFuzzerTestOneInput(const unsigned char* data, size_t size) {
                                        /*RequiresNullTerminator=*/false)));
 
   llvm::raw_null_ostream null_ostream;
-  Driver driver({.fs = fs,
-                 .installation = install_paths,
-                 .input_stream = nullptr,
-                 .output_stream = &null_ostream,
-                 .error_stream = &null_ostream,
-                 .fuzzing = true});
+  Driver driver(fs, install_paths, /*input_stream=*/nullptr, &null_ostream,
+                &null_ostream, /*fuzzing=*/true);
 
   // TODO: Get checking to a point where it can handle invalid parse trees
   // without crashing.