[clang] [clang][analyzer] Extend lifetime of dynamic extent information (PR #163562)

[Balázs Kéri via cfe-commits]

balazske wrote:

With the current version the extent symbol should become "dead" (not live any more) if the memory region becomes dead. The liveness of the extent symbol does not have effect on the liveness of the memory region. If the leak of the memory region can be detected, the leak of the extent can be detected too (maybe at a later point than before the patch). Normally the extent symbol is not something that can leak so this is anyway a rare case. Purpose of this patch is only to have the information about extent of the memory region available. If the original symbol would be garbage-collected but we keep it live like in this patch, it is not expected that the applied constraints change later. It should work like creating a new symbol for the extent and applying the constraints of the original symbol to it (and not making the original live). 

https://github.com/llvm/llvm-project/pull/163562