PLAYGROUND3D: Make various improvements

[BallM4788]

• Implement Tests 2 and 4 in the OpenGL Shaders renderer
• In Test 4, make sure the red square is completely out of view before it is warped from the top-right corner to the bottom-left corner.
• Left-clicking the screen starts the next test. For example, left-clicking when Test 1 is running will start Test 2; if Test 5 is the current test, the cycle will loop back to Test 1. This eliminates the need to recompile every time you want to do a different test.

[aquadran]

last 2 commits can be squashed to previous commits

[BallM4788]

Forgot to add the new fragment/vertex files to devtools/create_project/xcode.cpp and dists/scummvm.rc.