Lint suggestion: write to raw pointer with drop glue

One of the subtle aspects of *ptr = val where ptr is a raw pointer is that this will drop the old contents stored behind that pointer. On the one hand that might not be surprising because this is the same for mutable references, but on the other hand raw pointers are often used to point to invalid/uninitialized data, and then this is an easy way to cause a double-drop or to drop some garbage data. I have made this mistake myself and seen it a few times "out there".

So I think it'd be a good idea to lint against *ptr = val when ptr: *mut T and T has drop glue. The lint should recommend to use ptr.write(val) instead, which does not drop. Code that wants to drop should explicitly do ptr.drop_in_place().

The issue names no files, tests, or entry points. Start by locating Clippy's raw-pointer assignment lint infrastructure and its existing test patterns; done means assignments through raw pointers to types with drop glue are diagnosed, with suggestions to use write or drop_in_place as appropriate.