Before this commit, initModelTypes always looked at uses of each
instructions to see if its knowledge of the instruction's model type
could be improved.
This is useful in some cases, but it's detrimental when building model
casts, because this requires to see the exact type computed for an
instruction.
This commit introduces a new function initModeTypesConsideringUses,
which works like old initModelTypes, considering uses.
In this way we can make sure that uses are considered when necessary,
like when computing types to build new local variables, and ignored when
necessary, e.g. when building model casts.
Pietro Fezzardi