Allow Building the Editor with 3D disabled

[WhalesState]

• PR: Allow building the editor with 3D disabled, or without 3D Physics/Navigation. godot#105579

Benchmark by only one run for each builds using the same build flags and the editor loads faster by ~3.35 seconds with 3D disabled.

Section	3D Disabled	3D Enabled	🔍 Difference
Main::Start	6041.822 ms	7398.241 ms	+1356 ms
Editor	5967.604 ms	7329.662 ms	+1362 ms
Main::Setup2	1916.143 ms	2146.563 ms	+230 ms
Servers (Startup)	1442.803 ms	1594.149 ms	+151 ms
Scene (Startup)	301.489 ms	327.418 ms	+26 ms
Display Server	1165.205 ms	1265.940 ms	+100 ms
Rendering	85.439 ms	103.915 ms	+18 ms
Register Scene Types	119.242 ms	146.132 ms	+27 ms
Editor Modules/Ext.	0.058 ms	0.415 ms	+357%

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Benefits.

• Faster builds and smaller binaries: With 3D disabled, the build was faster by 25% and smaller by nearly 30mb, this enables indie developers and contributors targeting 2D-only projects to build the editor faster and generate smaller binaries, reducing complexity. It’s especially valuable for Android editor builds and other constrained environments. It also helps ensure that internal documentation and class listings reflect only the available 2D features, giving users a clearer view of what they can actually use when 3D is disabled.

• Cleaner and more focused UX for 2D developers: Currently, 3D features are only hidden via the feature profiler, they're still loaded, which adds overhead. With proper 3D disabling at the build level, developers can launch the editor into a truly 2D-focused mode. This improves usability, reduces distraction, and speeds up iteration. It's also a step toward fully disabling 3D drawing methods in the RenderingServer, which will further optimize the workflow for 2D game development.

• Reduced memory and resource usage: From past experience working on this, I’ve seen firsthand how disabling 3D can significantly lower memory consumption, making the editor more viable on low-spec machines or mobile setups. This can position Godot more favorably when compared to other lightweight 2D engines.
  Note: The reduction in memory usage is less by nearly 150mb which isn't much, so we still need a better comparison.

• Improved modularity and maintainability: This direction aligns well with Godot’s modular architecture. Adding clean, optional 3D support at the editor level increases the engine’s flexibility and opens the door to more specialized editor builds in the future.

• Improve 3D disable for templates: This will result in a faster testing and debugging for templates, and by working on this, I have spotted some issues related to the templates and fixed them in the PR, it was so easy to find those issues by adding some nodes to the scene tree in the editor.

Note: This will also allow generating C# bindings for 2D templates.

Related issues:

• Use 3D related nodes in editor causes runtime issue with disable_3d = true export template godot#103315