Fix dangling pointer issue in LocalUpdatbleMaps

Libunwindstack would remove duplicated items and update the `prev_map`
during reparsing `/proc/self/maps`. But we leave `prev_real_map`
pointing toward a MapInfo that will be deleted soon. It will cause a
dangling pointer issue.

Add new tests to cover this dangling pointer issue.

Bug: 155511785

Test: libunwindstack_test
Change-Id: I62e1b97bcb73f07e9349671f0b758f5ec9de16c0