Implement OS-level clipboard support to enable copy and paste between program instances

[mfaizsyahmi]

Currently bspguy just seem to use its internal memory for copy and paste operations. If it can instead use the OS clipboard, it'd be possible to do such operations between instances of the program.

The case use being the ability to copy and paste point and brush entities between maps, making a prefab placement workflow possible where you copy prefabs from a prefab map then pasting them into maps. Obviously there would be lighting mismatch but that's outside the scope of this post.

this library looks like a good candidate: https://github.com/dacap/clip

[mfaizsyahmi]

There has been a janky workaround in UnrealKaraulov's fork in which you export and import the bsp models. However the latter feature turned out to be misleading as it only references the bsp model files instead of properly embedding them, and that doesn't work on vanilla HL. Plus you wouldn't be able to duplicate the model and apply custom texlights that way.

[UnrealKaraulov]

imgui already has this feature