Add braces to C++ single-line loops and conditionals (NFC) (#2973)

This makes code easier to read and more consistent between C++ and Java.
Also update clang-format settings to always add a line break (even if no braces are used).

glass/src/lib/native/cpp/Model.cpp

@@ -6,4 +6,6 @@
 
 using namespace glass;
 
-bool Model::IsReadOnly() { return false; }
+bool Model::IsReadOnly() {
+  return false;
+}