Swift: split generated C++ code into .h and .cpp

swift/codegen/templates/cpp_classes_cpp.mustache

@@ -0,0 +1,37 @@
+// generated by {{generator}} from {{source}}
+// clang-format off
+#include "./TrapClasses.h"
+
+namespace codeql {
+{{#classes}}
+
+void {{name}}::emit({{^final}}TrapLabel<{{name}}Tag> id, {{/final}}std::ostream& out) const {
+  {{#trap_name}}
+  out << {{.}}Trap{id{{#single_fields}}, {{field_name}}{{/single_fields}}} << '\n';
+  {{/trap_name}}
+  {{#bases}}
+  {{ref.name}}::emit(id, out);
+  {{/bases}}
+  {{#fields}}
+  {{#is_predicate}}
+  if ({{field_name}}) out << {{trap_name}}Trap{id} << '\n';
+  {{/is_predicate}}
+  {{#is_optional}}
+  {{^is_repeated}}
+  if ({{field_name}}) out << {{trap_name}}Trap{id, *{{field_name}}} << '\n';
+  {{/is_repeated}}
+  {{/is_optional}}
+  {{#is_repeated}}
+  for (auto i = 0u; i < {{field_name}}.size(); ++i) {
+    {{^is_optional}}
+    out << {{trap_name}}Trap{id, i, {{field_name}}[i]};
+    {{/is_optional}}
+    {{#is_optional}}
+    if ({{field_name}}[i]) out << {{trap_name}}Trap{id, i, *{{field_name}}[i]};
+    {{/is_optional}}
+  }
+  {{/is_repeated}}
+  {{/fields}}
+}
+{{/classes}}
+}