zb/simplify

[zackbrown]

Milestone 1 of 2 for opening arbitrary projects with Pax Create (pax-designer)

• Remove need for .pax/pkg monorepo cloning and all of the complexity associated with it — no longer codegens onto filesystem via temporary crates; instead does all codegen during macro expansion, simplifying build process (note that we still generate .pax/cartridge.partial.rs in order to "hand off" from compiler + dynamic analysis to macro expansion)
• Change entrypoint crate from pax-chassis-* (which depended on userland crate via yet another crate pax-cartridge) to userland crate directly — removes pax-cartridge entirely as a crate and simplifies build process
• Remove pax_reexports and associated complexity; update module paths (including string representations) throughout monorepo
• Introduce platform feature flags to support userland crate-as-entrypoint, while keeping benefits of pax-chassis-* for platform-specific logic
• Refactor web, mac, and ios chassis + interface projects to support
• Refactor pax-std to remove pax-std-primitives as a separate crate and reorganize under functional buckets instead of primitives / components
• Refactor examples to support
• Subtree merge pax-designtime from paxcorp monorepo, preserving revision history and making open-source

[warfaj]

LGTM. Hit some version mismatching with wasm-bindgen across the various crates. I brought them all up to the highest version and it seemed to resolve the issue. Pushed a commit.

Great work!