Add support for VK_EXT_layer_settings

[thefishlive]

Prevously vkb::InstanceBuilder had support for changing settings in VVL via the VK_EXT_validation_features and VK_EXT_validation_flags extensions.

Recently, these two extension have been deprecated and replaced with the VK_EXT_layer_settings extension, which also allows for generic support for settings in any enabled layer.

This change adds support for setting layer settings when creating an instance with vkb::InstanceBuilder via the VK_EXT_layer_settings extension.