oleaut32: Initialise more of the context passed into user marshal functions in the tests for these functions.

Enable unmarshall testing for LPSAFEARRAYs and BSTRs which works on
Windows now that enough of the context has been filled in.

ole32: Initialise more of the context passed into user marshaling functions in the tests for these functions.

mlang: Implementation of base functionality of IMultiLanguage2::ValidateCodePage and IMultiLanguage2::ValidateCodePageEx.

Does not handle automatically installing language packs.
With help from Dmitry Timoshkov.