add `NATIVEAOT` constant when publish aot

### Is your feature request related to a problem? Please describe.

When publish with AOT, add a constant `NATIVEAOT` so that we could do aot-specific operation likes

```c#
#if NATIVEAOT
// .. aot-only
#endif
```

### Describe the solution you'd like

When `PublishAot` is `true`, define additional constant

```xml

$(DefineConstants);NATIVEAOT

```

### Additional context

see comment:
https://github.com/dotnet/runtime/discussions/109005#discussioncomment-10980398