Add RD_ENABLED when VULKAN_ENABLED or D3D12_ENABLED is added

[jsjtxietian]

Fixes #86411

In #83452, @RandomShaper changed the following line to use RD_ENABLED instead of VULKAN_ENABLED and D3D12_ENABLED

godot/core/config/project_settings.cpp

Lines 98 to 101 in 9d1cbab

	#ifdef RD_ENABLED
	features.append("Forward Plus");
	features.append("Mobile");
	#endif

But as far as I can see, RD_ENABLED is only defined in driver/vulkan and dx12, I'm not familiar with scon but I guess the definition there only affects the subfolder and so the editor failed to have this macro defined? Feel free to correct me.

Since I dont think revert this line is a good change as godot might support other backend for rd, this pr is a safeguard as I add RD_ENABLED when VULKAN_ENABLED or D3D12_ENABLED is added in detect.py, I might miss some places. Thank you for your help in advance.

[RandomShaper]

I wonder if all this could be managed at a more centric spot. Aside, this looks good to me. I think env.Append(CPPDEFINES=["RD_ENABLED"]) can be removed from drivers/vulkan/SCSub and drivers/d3d12/SCSub. I think they weren't contributing anything in the end.

[jsjtxietian]

I think env.Append(CPPDEFINES=["RD_ENABLED"]) can be removed from drivers/vulkan/SCSub and drivers/d3d12/SCSub

Done.

[qwofford]

This PR removed the error about Forward+ when launching a new project for me. I've read the documentation about Forward+, but it's still not clear to me exactly what it is. Is it Vulkan? A combination of tools?

I would like to test that my Forward+ is working correctly, now that this PR fixes the error message itself. I am able to load a 3D scene and interact with it, and the top right entry of my toolbar reads "Forward+". Is that sufficient evidence that things are working as intended?

[jsjtxietian]

I've read the documentation about Forward+, but it's still not clear to me exactly what it is.

https://docs.godotengine.org/en/stable/contributing/development/core_and_modules/internal_rendering_architecture.html

I guess you can understand it as a combination of fancy technologys that applys well on normal desktop hardware

the top right entry of my toolbar reads "Forward+"

I believe yes

[akien-mga]

I'm surprised that the original code doesn't work, appending to env should affect the base environment everywhere. Maybe it needs an Export("env")?

Anyway, this makes things consistent with how VULKAN_ENABLED and D3D12_ENABLED are registered so this change seems fine.

[akien-mga]

Thanks!

[jsjtxietian]

I wonder if all this could be managed at a more centric spot.

I'm thinking about if we can do something like, if VULKAN_ENABLED or D3D12_ENABLED enabled, add RD_ENABLED to CPPDEFINES.