[Remarks] Provide more information about auto-init calls

This now analyzes calls to both intrinsics and functions.

For intrinsics, grab the ones we know and care about (mem* family) and
analyze the arguments.

For calls, use TLI to get more information about the libcalls, then
analyze the arguments if known.

```
auto-init.c:4:7: remark: Call to memset inserted by -ftrivial-auto-var-init. Memory operation size: 4096 bytes. [-Rpass-missed=annotation-remarks]
  int var[1024];
      ^
```

Differential Revision: https://reviews.llvm.org/D97489