Add LZ4 compression support

[Hunam6]

Describe the project you are working on

I'm working on making a Minecraft client, I'm currently parsing the region files.
In order to do that I need to decompress LZ4-compressed bytes.

Describe the problem or limitation you are having in your project

Godot doesn't support this compression format/algorithm. I would like to have it supported in order to use it with the convenient utility functions Godot offers PackedByteArray.compress and PackedByteArray.decompress.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

I wouldn't be able to parse LZ4-compressed maps.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

godotengine/godot#100866

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

No, although if we ignore usage with builtin utility functions PackedByteArray.compress, PackedByteArray.decompress and FileAccess.open_compressed, it can probably be implemented as a GDExtension.

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

In the gaming industry, it's used in Nintendo Switch, Unity, Hitman 3, Death Stranding, Battlefield 4, Guild Wars 2, Crytek, Black Ops 3, Black Ops Cold War, FIFA, Sine Mora and 1000 Tiny Claws. (source: https://lz4.org/#lz4usedby).

Also, PackedByteArray.compress, PackedByteArray.decompress and FileAccess.open_compressed couldn't be used.