ole32: In simple create mode the size returned by IStream_Stat is actually the current stream position.

This avoids allocating them on the heap, and avoids the need for a
separate vtbl.

rpcrt4: Return the stack size from the ObjectStubless function so that the thunks are independent from the number of arguments.

user32/tests: Make some sysparams registry key optional, and fix some other failures on old Windows platforms.

user32/tests: Remove tests for internal DDE handle format, we don't care how the handles are implemented.

Our current code enumerates 145 Rfc1766 entries, so use a more
resonable start value.