CPP13 — Generic extraction of Fixed

Summary:
The C++ mapping does not permit extraction of a Fixed from an Any
in a generic way – I must always specify matching digits and scale in
order to call Any::to_fixed(). This is inconvenient if an application
wants to deal with Fixed values generically (because Fixed is a generic
type in C++ anyway).

Proposal:

Add an overloaded >>= operator for extraction of Fixed from an Any.
The operator sets the Fixed value to whatever scale and digits
are present in the type code.

Cheers,

Michi.