Adds a generic helper class that implements the XScriptContext interface. This interface is used in the providers to provide the XSCRIPTCONTEXT builtin variable. For example for the Python provider it is implemented in Python code. This C++ implementation can be reused by any script providers. Change-Id: I56f23138179555dee84ebf368e8a10cfb2fb4066 Reviewed-on: https://gerrit.libreoffice.org/c/core/+/205121 Reviewed-by: Neil Roberts <nroberts@libreoffice.org> Tested-by: Jenkins