Refactor instance extension and layer handling

[asuessenbach]

Description

Refactors the instance extension and layer handling.
Simplifies getting the "optimal" set of validation layers by just using VK_LAYER_KHRONOS_validation, assuming this is everywhere available nowadays.
Essentially is a different approach to #780 and would replace that PR.

Build tested on Win10 with VS2022. Run tested on Win10 with NVidia GPU.

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[SaschaWillems]

Not sure on this. It does work, but introduces a fundamental behavior change:

You can no longer run samples if the validation layers are not installed. If the requested layers are not found, an exception is thrown and the sample exits.

On main (before this change), you only get a debug message telling that the layer is not available, but the sample continues to run.

[asuessenbach]

@SaschaWillems With what sample do you get that exception?
I would expect to just get some informational output (-> instance.cpp, line 159, for example).

[SaschaWillems]

Sorry, should've mentioned that. Tested wit the hello triangle sample, and with this PR it throws an exception when it can't find the validation layers and then crashes for me.

[asuessenbach]

I see...
Before, the call to vkb::get_optimal_validation_layers returned a list of supported layers. Maybe some older layers, or even an empty list. And that list is checked again right after that.
I will simplify that a bit, assuming nowadays you just want VK_LAYER_KHRONOS_validation or nothing.

[SaschaWillems]

Thanks for the change. The samples that did their own validation layer checking now also work properly 👍🏻

[gpx1000]

Thanks for the PR. I have a question. Does this architecture handle optional extensions? (i.e. if an extension exists enable it, if it doesn't still allow for the sample to continue but report that the extension isn't enabled?). #780 seeks to handle the use case of allowing for optional extensions.

[asuessenbach]

Does this architecture handle optional extensions?

Yes it does, as you can see for example in instance.cpp, lines 222-238:

	for (auto requested_extension : requested_extensions)
	{
		auto const &extension_name        = requested_extension.first;
		auto        extension_is_optional = requested_extension.second;
		if (!enable_extension(extension_name, available_instance_extensions, enabled_extensions))
		{
			if (extension_is_optional)
			{
				LOGW("Optional instance extension {} not available, some features may be disabled", extension_name);
			}
			else
			{
				LOGE("Required instance extension {} not available, cannot run", extension_name);
				throw std::runtime_error("Required instance extensions are missing.");
			}
		}
	}