Expose Image.load_{format}_from_buffer() for OpenEXR

[paulherman]

Describe the project you are working on:
Trying to provide a clone of another game (MU).

Describe the problem or limitation you are having in your project:
The original game uses BMP and TGA files for textures.

Describe the feature / enhancement and how it helps to overcome the problem or limitation:
Exposing Load.*FromBuffer for said formats. This is already implemented in the core of the engine so just wiring is needed.

Describe how your proposal will work, with code, pseudocode, mockups, and/or diagrams:
Add another function pointer in the Image class and initialize it in the constructor of the two formats (just like for JPEG).

Probably more wiring is needed in places like this.

If this enhancement will not be used often, can it be worked around with a few lines of script?:
Not sure.

Is there a reason why this should be core and not an add-on in the asset library?:
The API should be uniform.

[Calinou]

Since BMP and TGA formats are supported via modules (rather than built-in drivers), this is probably not trivial.

[fire]

Are you able to get exr working too?

Use case loading exr at runtime for hdr terrain textures and other forms of bit packing buffers into hdr.

[Anutrix]

BMP done in godotengine/godot#42947.

[Calinou]

For Image.load_exr_from_buffer() to be implemented, the OpenEXR module would have to be compiled in release templates. Unfortunately, doing so would increase binary size by about 200 KB, which is non-negligible when targeting mobile and web platforms where fast downloads are paramount to a good experience.

The same problem also applies to making Image.save_exr() work in non-editor builds.