graphics/vkd3d: convert EXAMPLES to subpackage

[jbeich]

Summary

Similar to D43612 and bc458f82047a. Avoid pulling X11 dependencies by default.

Test Plan

Runtime tested inside jail with X11 socket passed through.

$ poudriere testport -j 132amd64 graphics/vkd3d
[...]
=>> Checking shared library dependencies
 0x0000000000000001 NEEDED               Shared library: [libSPIRV-Tools-shared.so]
 0x0000000000000001 NEEDED               Shared library: [libc.so.7]
 0x0000000000000001 NEEDED               Shared library: [libdl.so.1]
 0x0000000000000001 NEEDED               Shared library: [libm.so.5]
 0x0000000000000001 NEEDED               Shared library: [libncursesw.so.9]
 0x0000000000000001 NEEDED               Shared library: [libthr.so.3]
 0x0000000000000001 NEEDED               Shared library: [libvkd3d-shader.so.1]
 0x0000000000000001 NEEDED               Shared library: [libvkd3d.so.1]

$ poudriere testport -j 132amd64 graphics/vkd3d~examples
[...]
=>> Checking shared library dependencies
 0x0000000000000001 NEEDED               Shared library: [libc.so.7]
 0x0000000000000001 NEEDED               Shared library: [libdl.so.1]
 0x0000000000000001 NEEDED               Shared library: [libm.so.5]
 0x0000000000000001 NEEDED               Shared library: [libvkd3d-utils.so.1]
 0x0000000000000001 NEEDED               Shared library: [libvkd3d.so.1]
 0x0000000000000001 NEEDED               Shared library: [libxcb-keysyms.so.1]
 0x0000000000000001 NEEDED               Shared library: [libxcb.so.1]