Leaving room for experimental features.

[mighdoll]

We want people to try making experimental features in wesl linkers as a way to validate feature ideas that we might eventually stabilize into a standard wesl edition.

But it'd be nice if at some experimental features wouldn't break other tools (language servers, prettifiers, etc.). Can we design in some room in the standard wesl syntax for unrecognized extensions?

For example, we could allow unrecognized @ attributes extensively in the syntax.

[ncthbrt]

Another important aspect of this is the design of our compilers and other tools. If we want to support this, they'll need to be extensible and modular themselves.