dip1000 and preview in combine to cause extra safety errors

[Dennis]

On Thursday, 9 June 2022 at 01:18:30 UTC, Steven Schveighoffer 
wrote:
> For some reason, while you can't return a pointer to a local, 
> you can return a scope pointer.

A pointer to a local is guaranteed to be a dangling pointer when 
you return it, while a `scope` pointer is not guaranteed to be 
memory with limited lifetime when you return it. `scope` is only 
a conservative compile-time approximation of what's actually 
happening, which makes it susceptible to false positives:

```D
int* f(int x) @safe {
     int* p = &x; // p is inferred scope here
     p = new int; // p is no longer pointing to stack memory
     return p;    // Error: scope variable `p` may not be returned
}
```
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