Use these to implement a few helper functions. Change the type
verification in type accessor functions to use these new functions.

widl: Add a new function, type_alias_get_aliasee to wrap  the retrieval of the type that the alias aliases.

comdlg32: We need to be able to type the decimal separator into the margin edit controls so ES_NUMBER is no use. Subclass them and filter WM_CHAR instead.

comdlg32: Set the margins groupbox title to reflect whether we are using metric or imperial measurements.