Is your feature request related to a problem? Please describe.

Applications should have a way of figuring out if they can render to a particular format of image.

Describe the solution you'd like

Add a field to what format.describe() returns that tells you if it is renderable.

Describe alternatives you've considered

This would need to be a massive match on the users sid

If the hello_triangle example is changed slightly to only draw the triangle once, and we change the color attachment's load_op to wgpu::LoadOp::Load instead of Clear, my expectation is that the result is the same, except that the green clear color is gone. However the result is that the red triangle only shows up every other frame, with blank frames in between.

Is this expected behavi