If comparing a DynamicGeodeticReferenceFrame object and its export to
WKT1, which is a simple DATUM object, currently in non-strict comparison
mode, we'd consider the datum to be equivalent to the dynamic datum, but
not the reverse, which breaks the symmetric property of the
isEquivalentTo() operation. So fix this, to consider both equivalent
whatever the operand order.
(in strict mode, the objects will be considered different of course)

Spotted in the GDAL GeoTIFF CRS reader code:
https://github.com/OSGeo/gdal/blob/f9d48bdcc8c90df20e53b5af5785f1e5d78910db/frmts/gtiff/gt_wkt_srs.cpp#L832

Do same change for vertical datum vs dynamic vertical datum.

If window.h is included in the same compilation unit we can expect this kind of errors:
```
util.hpp:348:15: error: expected identifier before ‘,’ token
  348 |         STRICT,
```

- Remove the explicit PROJ_MSVC_DLL_IMPORT symbol used for importing
  symbols from a MSVC .dll: by default on MSVC, we use
  now __declspec(dllimport), unless PROJ_MSVC_DLL_EXPORT is defined
  by PROJ at build time. This makes it easier for users: they
  don't have to define anything special. This simplifies in particular
  the build of our binaries
- For static builds, export -DPROJ_DLL= as public, so that users
  that import PROJ through CMake mechanism don't have to do it
  manually.