Rename "GPU memory size" to "Min GPU memory size"

[lexaknyazev]

Rationale:

1. When compressed transcode targets are not available, KTX textures will be decoded to RGBA8 thus matching the uncompressed size (the same as PNG / JPEG).
2. On desktop platforms, opaque ETC1S may be transcoded to BC7 that uses 16 bytes per block.

[donmccurdy]

Since this column name also applies to PNG/JPG textures, and the GPU memory size estimates there are assuming expansion to RGBA8, wouldn't a "minimum" size need to be lowered for PNG/JPG? I guess the alternative would be something like "estimated GPU memory size"?

[lexaknyazev]

"Estimated" is too vague, but I don't have any better proposals.

• PNG / JPG are always expanded to RGBA8 on platforms that use D3D or Metal.
• On OpenGL or Vulkan desktops, only Intel hardware may directly support 24-bit pixels, other vendors expand them in-driver, IIRC. Some mobile GPUs do support RGB8 natively, though.
• Transcoded size of single-slice opaque ETC1S on desktops is a matter of choice. We recommend BC7 (16 bytes per block) as it's gives less transcoding loss than BC1 (8 bytes per block) although the latter is a still a valid option.

[donmccurdy]

Updated output, example below:

---

TEXTURES ────────────────────────────────────────────	#	name	uri	slots	instances	mimeType	resolution	size	gpuSize¹
0		baseColor.ktx2	baseColorTexture	1	image/ktx2	512x512	123 KB	456 KB

¹ gpuSize estimates minimum GPU memory allocation. Older devices may require additional memory for GPU compression formats.