encoder: rename cuCoder to analysis for better clarity

the data type of cuCoder changed from TEncCu to Analysis weeks ago
predict: inline single call of predInterBi()
predict: inline predInterUni(), getWpScaling() and simplify motionCompensation()

After this refactor, motionCompensation no longer needs the cu parameter. It
was only used to pass to another member function to gain access to cu->m_slice
which is now a member variable.

This refactor removed a number of arguments to addWeightBi and addWeightUni
which were always member variables.
predict: remove check for reallocations, comment nits

we don't do this anywhere else; there would be huge leaks if the Search object
were initialized multiple times. there's no reason to check here.
predict: combine and check allocations and return failures
predict: split weighted prediction values from WeightParam

The arguments passed to addWeightBi() and addWeightUni() are just the
"w, o, offset, shift, round" integers. They don't need the fields which were
signaled in the slice header or vice-versa.