V4 custom shader batching support

[rh101]

Changed ProgramType IDs to be uint32_t, so that users can specify their own custom ID. This will enable users to batch custom shaders.

Note that the changes do not affect the operation of the built-in types or CUSTOM_PROGRAM type. The code only comes into effect when users set their own ID via Program::setProgramType() and optional ProgramState::setBatchId (for ProgramStates with different uniform values).

An example:

const uint32_t uniqueCustomShaderId = 1234;

auto* fileUtils = cocos2d::FileUtils::getInstance();
const auto fragmentFullPath = fileUtils->fullPathForFilename(path);
const auto fragSource = fileUtils->getStringFromFile(fragmentFullPath);
auto* program = Device::getInstance()->newProgram(cocos2d::positionTextureColor_vert, fragSource);
program->setProgramType(ProgramType::CUSTOM_PROGRAM | uniqueCustomShaderId);

auto* programState = new (std::nothrow) ProgramState(program);
programState->setBatchId(1); 

// These sprites use the same uniform values, both have batch ID = 1
sprite1->setProgramState(programState);
sprite2->setProgramState(programState->clone());

// Create a new cloned ProgramState that will have different uniform values
auto programState2 = programState->clone();
programState2->setBatchId(2);
// These sprites use the same uniform values, both have batch ID = 2
sprite3->setProgramState(programState2);
sprite4->setProgramState(programState2->clone());

This gives the users the flexibility of providing their own custom shaders while still allowing the nodes using them to be batched.

[rh101]

If anyone has any suggestions on how to implement this differently to achieve the same outcome (supporting batching with custom shaders), then please do put your ideas forward.