Extent2D and Extent3D should implement IEquatable

# Summary of feature
Silk.NET.Vulkan.Extent2D and Silk.NET.Vulkan.Extent3D should implement IEquatable.

# Comments

There might be other structs that would benefit from the implementation.

In my code I'm comparing 2 Silk.NET.Vulkan.Extent2D with `currentSize.Equals(displaySize)` to check if some resources should be recreated.
As a workaround i changed my code to compare the individual fields.

Output from resharper code inspection:
```
warning: Struct 'Extent2D' is checked for equality using the inefficient runtime-provided implementation
Default implementations of the 'Equals' and 'GetHashCode' methods of a struct are reflection-based and bad-performing
```