Move lots of code for creating the VariableClassification
into a separate builder class.
Make all collections in VariableClassification immutable,
they are handed out to callers all the time.

With this change,
the VariableClassification is not created lazily anymore.
Most analyses need it anyway, so we do normally do not save time on lazy
creation.
Lazy creation complicates things, for example exceptions are not handled
properly currently, and the timing statistics of CFA creation
do not contain the time for creating the VariableClassification.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@14472 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c