proposal: support for automatic presentation modes

[rajveermalviya]

wgpu recently made changes to presention api, which removes implicit fallback for unsupported presentation modes.

it now allows three new presentation modes:

• FifoRelaxed
• AutoVsync : FifoRelaxed if available, otherwise fallback to Fifo
• AutoNoVsync : Immediate or else Mailbox or else Fifo

it also adds a companion method for listing supported presentation modes for a surface.
for webgpu.h it can be:

WGPUPresentMode const * wgpuSurfaceGetSupportedPresentModes(WGPUSurface surface, WGPUAdapter adapter, size_t * count);

so can we add these three present modes & this function to webgpu.h ?

for more info check:
https://github.com/gfx-rs/wgpu/blob/c36eb9f44bd9462fe176fb859839592131428feb/wgpu-types/src/lib.rs#L2951-L3021

also cc @cwfitzgerald @jimblandy

[rajveermalviya]

closing in favor of #197