Tests: Refactor GenerateExportHeader test code

Refactor the library code used in the GenerateExportHeader test to use
an improved naming convention that more directly identifies what it
being tested, making use of namespaces to avoid possible symbol
collisions. This also eliminates duplicate cases such as `libshared()`
and `libshared_not_exported()` which had the same decoration, and adds
consistent pairings of <name>_EXPORT and <name>_DEPRECATED_EXPORT which
were missing previously. The data tests from the previous commit are
also added to `libstatic` and `libshared_and_static` for consistency.

Note that there are no exported members of exported classes, as these
are not allowed on Windows.