Put TGA decoder into its own crate #108

Job	Run time
Build WebGL Example (ubuntu-latest)	51s
Build [OpenGL \| Linux (x86)]	1m 1s
Build [OpenGL \| Linux (ARM)]	1m 18s
Build [OpenGL \| MacOS (x86)]	1m 56s
Build [OpenGL \| MacOS (ARM)]	1m 29s
Build [OpenGL \| Windows (x86)]	1m 35s
Build [WGPU \| Linux (x86)]	1m 36s
Build [WGPU \| Linux (ARM)]	1m 55s
Build [WGPU \| MacOS (x86)]	3m 14s
Build [WGPU \| MacOS (ARM)]	3m 51s
Build [WGPU \| Windows (x86)]	3m 29s
	22m 15s

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