D3D11: Expose swapchain flags & wrapping fix

• swapchain flags

Allow specifying additional flags to use when creating the swapchain. This allows creating eg. a waitable swapchain for additional control over presentation timing.

- bind flags

When using video texture formats (eg. NV12/P010), D3D11 does not allow creating multiple conflicting views of a texture at the same time, which causes texture wrapping to fail if libplacebo tries to map both a shader view and a render target view from such a texture.

Unfortunately, libplacebo does not have enough information to know if it should just read from a wrapped texture, or also render to it, instead give the user the control to mask out certain bind flags and prevent libplacebo from using them.