Loader now generates a struct that contains of bools for each instance
extension and a function to set the bool to true if the extension is in
the list passed in. This consolidates that logic into one place rather
than having it spread out across the codebase. It also enable further
changes that will require each drivers list of supported instance
extensions.

Make sure that the surface extension is supported by a driver and
enabled before calling down on each surface creation function. This
fixes crashes where a driver on the system doesn't support a surface
extension that the application is using but still exposes the function
pointer.

Renames `instanceExtensions` to extensions to reflect that it is all
extensions, not just instance.
Uses self.extensions instead of creating local variables.

The Vulkan-Loader now doesn't call into drivers if they do not support the
extension that was used to create the VkSurfaceKHR handle. This prevents
crashes from occuring where a driver is called using a surface that it does
not know about, due to the driver not supporting the surface extension.

Because the specification requires that VkSurfaceKHR must be a valid handle,
the loader should not allow calls down into drivers which cannot know about
the surface. Instead it should "emulate" the call as appropriate, returning
0 for counts and setting to 0 any structures that were passed in.