Added ConvertTo<*> methods in exec.cpp, and eval_<*> methods in express.cpp
Added Eval(Optional)ExprAs<Type>() methods in exec.cpp, where <Type> = BooleanRef, DataRef, etc
[[ RefactorSyntax ]] EP-less implementation of MCChunk::getobj added
[[ refactorSyntax ]] All MCChunk's EP-based functions replaced with EP-less ones
The EP-based methods are now based on an MCExecContext
[[ RefactorSyntax ]] MCChunk's functions using EP reverted
They were wrapping the new EC-based functions, but issues arose