[analyzer] Dump the environment entry kind as well

By this change the `exploded-graph-rewriter` will display the class kind
of the expression of the environment entry. It makes easier to decide if
the given entry corresponds to the lvalue or to the rvalue of some
expression.

It turns out the rewriter already had support for visualizing it, but
probably was never actually used?

Reviewed By: martong

Differential Revision: https://reviews.llvm.org/D132109