perf annotate: Save pointer offset in stack state

perf annotate: Save pointer offset in stack state

The tracked pointer offset was not being preserved in the stack state,
which could lead to incorrect type analysis. This change adds a
ptr_offset field to the type_state_stack struct and passes it to
set_stack_state and findnew_stack_state to ensure the offset is
preserved after the pointer is loaded from a stack location. It improves
the type annotation coverage and quality.

Signed-off-by: Zecheng Li <zecheng@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>