[Clang] Extend lifetime bound analysis to support assignments for the built-in pointer type (#96475)

The lifetime bound warning in Clang currently only considers
initializations. This patch extends the warning to include assignments.

- **Support for assignments of built-in pointer types**: this is done is
by reusing the existing statement-local implementation. Clang now warns
if the pointer is assigned to a temporary object that being destoryed at
the end of the full assignment expression.

With this patch, we will detect more cases under the on-by-default
diagnostic `-Wdangling`. I have added a new category for this specific
diagnostic so that people can temporarily disable it if their codebase
is not yet clean.

This is the first step to address #63310, focusing only on pointer
types. Support for C++ assignment operators will come in a follow-up
patch.

Fixes #54492

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