deqp/functional/gles3/es3fShaderDerivateTests.js read back with wrong format/type

The c++ side of the deqp tests takes into consideration if the framebuffer's internalformat is RGBA_INTEGER, then readPixels should adjust the format/type accordingly.

However, the js version always uses RGBA/UNSIGNED_BYTE, which causes INVALID_OPERATION in readPixels.

Start with deqp/functional/gles3/es3fShaderDerivateTests.js and inspect how its readPixels call selects format and type. Compare that behavior with the C++ deqp tests, especially for RGBA_INTEGER framebuffers. Done means the JavaScript test uses the matching format/type and no longer triggers INVALID_OPERATION in readPixels.

Written by the indexing model from the issue text.