[Analyzer][NFC] Move RangeConstraintManager's def before ConstraintAssignor's def

In this patch we simply move the definition of RangeConstraintManager before
the definition of ConstraintAssignor. This patch is exclusively needed for it's
child patch, so in the child the diff would be clean and the review would be
easier.

Differential Revision: https://reviews.llvm.org/D110387