Add tests for EM_POSFROMCHAR for 1.0 and 2.0.

As documented in DirectX7 SDK, d3d7 devices set FPU mode (control word) on every 
call and restore it back to original state before returning, if created in 
DDSCL_FPUPRESERVE cooperative mode. This allows games to work with FPU in a 
possibly incompatible mode and avoid resetting it all the time.

rpcrt4: Fix NdrConformantVaryingStructUnmarshall to use buffer memory if applicable and to reuse memory for embedded pointers.

rpcrt4: Factor out string validation from NDR unmarshalling functions into a separate function, validate_string_data.

Do so by calculating the alignment of members when iterating through
the structures and adding it onto the buffer and memory offsets.

Only call type_memsize once elsewhere in the embedded pointer
processing functions since the return value will be the same from the
second call.