[JVMCI] add methods to HotSpotVMConfigAccess to query instead of assert cpp type

The C++ type of a field accessed via HotSpotVMConfigAccess can change across JVMCI versions. Currently, there's no way to handle this in Graal without doing a bunch of ugly exception handling. The API should be extended to allow for getting the C++ type of fields so that the checking can be done by Graal.