Use doubles for time in many other places

[aaronfranke]

Follow-up to #38880 and a subset of #21922 split into its own PR for easier reviewing.

Single-precision floats should never be used for time, because it fails after a few days as errors accumulate over time. With doubles, this code should work for about 4.7 million years before failing, assuming 60 FPS.

Unlike #38880 which aims to solve a specific problem (#38878), this PR is just broadly replacing float with double in time APIs. This should not impact performance on 64-bit systems (or extremely little), the main downside is slightly increased memory usage.

An alternative implementation would be to use real_t, in which case this code would only work for more than a few days if Godot was also using doubles for vectors, though I think it's better to use doubles for time always.

[akien-mga]

Needs a rebase.

[akien-mga]

Thanks!

[MohammadKhashashneh]

@aaronfranke I'm fixing a PR regarding cumulative time to use doubles as well, and I noticed the binding of both _process and _physics_process in core/os/main_loop.main are still set as float.
shouldn't it be double as well?

[aaronfranke]

@MohammadKhashashneh Are you referring to this?

	BIND_VMETHOD(MethodInfo(Variant::BOOL, "_physics_process", PropertyInfo(Variant::FLOAT, "delta")));
	BIND_VMETHOD(MethodInfo(Variant::BOOL, "_process", PropertyInfo(Variant::FLOAT, "delta")));

It's a bit confusing, but Variant::FLOAT is actually C++ double, see core/variant/variant.h#L204.

[MohammadKhashashneh]

indeed!
Well, what about the documentation in doc/classes/Node.xml ? same story as well?

[aaronfranke]

@MohammadKhashashneh Yes. Variant only has 64-bit floats and ints, and this is what is bound and used in GDScript and other languages. If other sizes are used internally (such as C++ float) then it's automatically casted to and from Variant's internal type (aka C++ double in the case of floats). This type is named Variant::FLOAT in the binding and "float" in the docs.

[MohammadKhashashneh]

@aaronfranke well noted, thank you