#import "file" without list of names should err/warn

Import with a file path, but without a list of names, "fails" silently: ```wgsl #import "common.wgsl" ``` This syntax is very similar to C's `#include` that just imports *everything*, so I did not think of specifying individual type names, and was puzzled why this directive doesn't seem to do anything, and doesn't even cause a compilation error.