Enable compilation on Windows by exporting all symbols of shared libraries (as is done by default in Linux and macOS)

[traversaro]

This package compiles several shared libraries, but does not expose any symbol on Windows, so if the CMake project is compiled on Windows, no import library .lib is actually generated.

On Linux and macOS, everything compiles fine as by default all the symbols are visible. We can achieve exactly the same behavior in Windows by setting to ON the CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS CMake variable, so this PR sets the CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS variable to ON, to ensure that the compilation works fine on Windows.

[traversaro]

@JWhitleyWork if there is anything we can do to enable the merge of this PR, feel free to ask, thanks!