Snapshot clean ups

- Don't call eval() in mock_runtime - not allowed - see js2c.py.
- Don't use v8_use_external_startup_data
- Move MakeSnapshot to snapshot_creator.cc
- Use logging.h in from_snapshot.cc

deno2/mock_runtime_test.cc

@@ -99,5 +99,6 @@ TEST(MockRuntimeTest, SnapshotBug) {
 int main(int argc, char** argv) {
   testing::InitGoogleTest(&argc, argv);
   deno_init();
+  deno_set_flags(&argc, argv);
   return RUN_ALL_TESTS();
 }