[analyzer] InnerPointerChecker: fix displayed checker name.

For InnerPointerChecker to function properly, both the checker itself
and parts of MallocChecker that handle relevant use-after-free problems
need to be turned on. So far, the latter part has been developed within
MallocChecker's NewDelete sub-checker, often causing warnings to appear
under that name. This patch defines a new CheckKind within MallocChecker
for the inner pointer checking functionality, so that the correct name
is displayed in warnings and in the ExplodedGraph.

Tested on clang-tidy.

Differential Review: https://reviews.llvm.org/D50211

llvm-svn: 339067