Add IEEE 754 single/double precision support to wxDataStream classes.

Add IEEE 754 single/double precision support to wxDataStream classes.

Allow to optionally raed/write float/double values in IEEE 754 single/double
precision formats, respectively, instead of always using the extended
precision format for both of them.

This makes the code more flexible, allowing for better interoperability with
the other programs, and also allows to implement floating point functions in
these classes even when wxUSE_APPLE_IEEE is turned off (as can be the case
because of the licencing concerns for the code in extended.c).

Closes #10625.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73938 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775