[gles] Fix tex_sub_image_* calls not always adjusting to target texture

[daxpedda]

Connections
Fixes #3197.

Description
In GLES different arguments have to be passed into tex_sub_image_* calls depending on the target texture. Specifically cube maps, 2D texture arrays and cube map arrays. This was done correctly in some calls, specifically write_texture, but not in others.

This fixes it.

Testing
There was a test actually testing copy_external_image_to_texture for texture array, which was expected to fail, it succeeds now.

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Details

The following functions now take the array index into account (only listing changes):

• copy_external_image_to_texture when targeting cube maps, 2D texture arrays and cube map arrays.
• copy_texture_to_texture when targeting 2D texture arrays and cube map arrays.
• copy_buffer_to_texture when targeting uncompressed cube map arrays.
• copy_buffer_to_texture when targeting compressed 2D texture arrays and cube map arrays.

Basically the change is to make sure that all calls to tex_sub_image_* take into account the following:

• If the target texture is a 2D texture array or cube map array, pass the array layer in the offset_z parameter.
• If the target texture is a cube map, pass the array layer in the target parameter.

[teoxoy]

Looks good but I think we should also handle TEXTURE_CUBE_MAP_ARRAY.

[daxpedda]

Looks good but I think we should also handle TEXTURE_CUBE_MAP_ARRAY.

Done! I also simplified the code a bit.

I updated OP with some details, would be great if you could confirm my assumptions.

[teoxoy]

This looks great; thank you!