[clang] [llvm] Adapted MemRegion::getDescriptiveName to handle ElementRegions (PR #85104)

[Balazs Benics via cfe-commits]

steakhal wrote:

> In addition to the above-mentioned issues there is also a conceptual problem with using `getOriginRegion()` to describe a symbol: it names the region where the symbol _originated_ (if it originated as the unknown initial value of a symbol), which is not necessarily the region where the symbol is stored _now_.
> 
> For example consider the (somewhat contrived) code
> 
> ```
> int matrix[10][10];
> int func(int x, int y) {
>   int tmp = x;
>   x = y;
>   y = tmp;
>   return matrix[x][-999]; 
> }
> ```
> 
> Here the checker alpha.security.ArrayBoundV2 (which uses `getDescriptiveName`) would report that
> 
> ```
> Access of 'matrix[y]' at negative byte offset
> ```
> 
> because the symbolic value of the index _originated from_ the parameter `y` (i.e. the symbol is identified as "this is the initial value of `y`).

I agree, but I don't see how this relates to this patch.
I think the original author of this code probably wanted to something what we propose here.
We can argue if that's a good thing or not, but that feels like a different topic to me.

https://github.com/llvm/llvm-project/pull/85104