Fix linking NavigationServer2D/3D with all classes disabled in build profile

[akien-mga]

For some reason the destructor for NavigationMeshSourceGeometryData2D/3D being implemented in the .cpp was causing linking issues.

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I was testing making minimal sized export templates with the following command:

scons target=template_release production=yes disable_3d=yes disable_advanced_gui=yes optimize=size deprecated=no minizip=no modules_enabled_by_default=no module_gdscript_enabled=yes vulkan=no wayland=no build_profile=blank.build lto=none

And this build profile which disables nearly all classes in the engine, generated from a blank project with just icon.svg, so that's the only type of resource it needs to support: blank.build.txt

I would get this linking issue:

/usr/bin/ld: servers/libservers.linuxbsd.template_release.x86_64.a(navigation_server_2d.linuxbsd.template_release.x86_64.o): in function `Ref<NavigationMeshSourceGeometryData2D>::Ref(Variant const&)':
navigation_server_2d.cpp:(.text._ZN3RefI34NavigationMeshSourceGeometryData2DEC2ERK7Variant[_ZN3RefI34NavigationMeshSourceGeometryData2DEC5ERK7Variant]+0x1f): undefined reference to `typeinfo for NavigationMeshSourceGeometryData2D'
/usr/bin/ld: servers/libservers.linuxbsd.template_release.x86_64.a(navigation_server_3d.linuxbsd.template_release.x86_64.o): in function `Ref<NavigationMeshSourceGeometryData3D>::Ref(Variant const&)':
navigation_server_3d.cpp:(.text._ZN3RefI34NavigationMeshSourceGeometryData3DEC2ERK7Variant[_ZN3RefI34NavigationMeshSourceGeometryData3DEC5ERK7Variant]+0x1f): undefined reference to `typeinfo for NavigationMeshSourceGeometryData3D'

I was puzzled to have this issue with NavigationMeshSourceGeometryData2D but not NavigationPolygon, when both are used as Ref<T> in NavigationServer2D. Comparing both classes, the main difference seemed to be the destructor implemented in the .cpp, and moving it solved the issue. The rest of the changes are just for consistency.

I don't really know why this fixes the linking issue, or why it happened before this fix. Maybe someone more versed in C++ can clarify :)

[smix8]

Not sure why or what but whatever works.

[AThousandShips]

Makes sense to me