Optim: DestImageGenInfo destSizeReciprocal_v2

• Replaced DestImageGenInfo’s `int destWidth`/`Height` with a pre-calculated `GLKVector2 destSizeReciprocal_v2` that getDestImagePixelBytes() now uses directly.
• Minor: getDestImagePixelBytes() now computes pixelST on its own line (good for debugging).
Minor: Changed GLKMathExtensions.inl file type

• `GLKMathExtensions.inl` was showing up as plain text in Xcode.  Changed to explicit “C Source”.
Minor: Added GLKVector2Lerp2() function

• Added a GLKVector2Lerp2() function to GLKMathExtensions— does what GLKVector2Lerp does except taking a vector2 for the `t`/ratio and processing each axis independently.
	» Like all of my GLKVector2 additions, doesn’t have a NEON-optimized variant.  Yet.
Minor: Updated genDestImagePixelBytes debug UV code

• Missed this earlier.  Updated genDestImagePixelBytes()’s debug show-UVs code with changed variable names.