ZIR-236: Create a new Zirgen Standard Library

[jacobdweightman]

[NOT URGENT FOR REVIEW]

It seems to me that there are four tiers of components, divided by importance and frequency of use:

1. Built-ins: the core building blocks that can't be implemented in Zirgen itself (e.g. NondetReg)
2. Preamble components: slight abstractions around built-ins that will almost certainly be used in every circuit (e.g. Reg)
3. Standard components: components that are likely to be sufficiently useful across many circuits, but the user should "opt-in" (e.g. OneHot<N>, BitReg, etc)
4. Everything else: circuit-specific things, "third party" component libraries, etc.

This PR takes a first pass at introducing a "standard library" for components of variety (3). The build system changes are minimal and this library isn't treated differently than others; the programmer still has to -I path/to/standard-library to use it. I leave that for future work, as it probably warrants discussions and possibly an RFC.