Support double precision

[Naros]

Supersedes #450

[Naros]

Hi @fire I have a new idea about double builds, from your point of view do we only need those for linux?

[fire]

I don't understand? double precision should be in theory built for all platforms.

[Naros]

Ok, that's what I was also thinking, but I wanted to be sure.

To automate the delivery of double-precision builds, I think we can simply build godot-engine with the double-precision flag and dump the two API files that are needed for building godot-cpp with double-precision. I tested this process and it works quite well, particularly when we cache the godot-engine build.

The main question is how to orchestrate the build on CI. Obviously, we could set up the CI job to build both precisions in a single matrix and distribute a single plugin archive that has both, but my concern is the archive bundle's size given we'd duplicate each job for Linux, Windows, macOS, Android32, Android64, and Wasm32.

I was thinking since Godot does not officially distribute double builds, would it make sense to distribute a separate plugin artifact that contains specifically just the double-precision builds instead. The new Update Picker would have to be adjusted to handle this whereas a single distribution wouldn't affect it.

Whats your $0.02 worth @fire ?

[fire]

I think there's a gap in how asset library handles double precision so the crucial thing is that I needed an official build of double-precision for my project, but the exact arrangement is up to you.

[aaronfranke]

The upstream godot-cpp has renamed this variable to GODOT_PRECISION: godotengine/godot-cpp#1583