[C++] flatc generates invalid code for union UnPackTo when "--cpp-field-case-style upper" and "--gen-object-api" are used

[Ailuridae]

The schema below, when compiled with the options --cpp, --gen-object-api and --cpp-field-case-style upper, generates invalid C++ code.

Affecfted versions: v24.3.25, current master

Schema

table MyUnionContent {
  value:uint8;
}

union MyUnion {
  content:MyUnionContent,
}

table MyTable {
  property:MyUnion;
}

Output

// ...

struct MyTableT : public ::flatbuffers::NativeTable {
  typedef MyTable TableType;
  MyUnionUnion Property{};
};

// ...

inline void MyTable::UnPackTo(MyTableT *_o, const ::flatbuffers::resolver_function_t *_resolver) const {
  (void)_o;
  (void)_resolver;
  { auto _e = Property_type(); _o->property.type = _e; }
  { auto _e = Property(); if (_e) _o->Property.value = MyUnionUnion::UnPack(_e, property_type(), _resolver); }
}

// The capitalization of _o->property.type and property_type() is wrong

// ...

[Ailuridae]

Related: #7210