Wire up wgsl_minifier as an option.

[Swoorup]

There is an hastily written code here to convert naga module to strings, which contains wgsl_minifier.

It should be wired up as a WgslBindgenOption instead. Currently the problem is for naga_oil we output a single generated wgsl for embedded source option. Unfortunately some features like pipeline constants aren't supported when writing the wgsl by naga.