Update tutorial snippet to pass proper varying from vertex shader to

[nickcosmo]

Resolves #1437

Description

This is a follow-up PR to this PR #1122 (review) where it was mentioned that the same fix should be applied to the 2.0 branch.

Changes

• Remove references to the vVertexColor varying in the tutorial snippet for "Varyings: Passing data from vertex to fragment shader" and instead pass vTexCoord varying to the fragment shader.
• Some white space changes to fix how the indentation and padding is displayed on the code blocks.

[nickcosmo]

@doradocodes @Nwakaego-Ego @davepagurek Follow-up PR to our previous discussion here -> #1122.

I also noticed that the code looks the same in the src/content/tutorials/ko/intro-to-glsl.mdx file. I can't read that one (guessing Korean?) but I can also update the code snippet there if it makes sense to do so. Just lmk!

[davepagurek]

Looks good, thanks again!