Add NUM_VALUES for enums and size for structs (see #3836)

API versioning requires that enumerations end with a count value
(`*_NUM_VALUES`) and structs begin with a size value (`size_t size`).
Wrapper templates are updated to support structs with different size
values indicating different versions.

To test:
Run `ceftests --gtest_filter=ApiVersionTest.StructVersion*`

libcef/browser/test/test_server_impl.cc

@@ -200,6 +200,9 @@ class CefTestServerImpl::Context {
         case CEF_TEST_CERT_EXPIRED:
           test_server_->SetSSLConfig(EmbeddedTestServer::CERT_EXPIRED);
           break;
+        case CEF_TEST_CERT_NUM_VALUES:
+          DCHECK(false);
+          return false;
       }
     }