Support floating-point atomics

[kvark]

Is your feature request related to a problem? Please describe.
See gfx-rs/wgpu-rs#564

I believe it is quite a fundamental component required for many compute operations.

Describe the solution you'd like
A native-only Feature corresponding to VK_EXT_shader_atomic_float Vulkan extension.
We also need to be better at validating SPIR-V capabilities.

Describe alternatives you've considered
Enabling this feature everywhere where it's available. This would be unfortunate, since it would harm portability.

Additional context
First, an investigation needs to be done to determine the platform support for this extension on different APIs.
Second, gfx-rs changes need to be done to enable it. Only then we can expose a feature here.

[kvark]

For an example of how other similar feature was added, see #754 and gfx-rs/gfx#3281