[Small] Check Node OS & Arch availability and support M1 native builds

[charlespierce]

Closes #34

Info

• Now that Rust 1.49 is out and has stable Tier 2 support for Apple M1 chips, we can create an M1 native build of Volta.
• Currently, Node doesn't provide pre-built binaries for M1 chips, so we still need to fetch the x64 version of Node and run it through Rosetta 2.
• At the same time, we should also confirm when resolving a Node version that it is available for the current OS & Architecture.

Changes

• Updated the NODE_DISTRO_* constants to also include NODE_DISTRO_IDENTIFIER, representing the identifier used in the Node index files property.
  • Currently this uses the osx-x64-tar identifier on M1 MacOS, since Node doesn't provide pre-built M1 binaries and hasn't yet indicated what the identifier will be).
• Updated the parsing of the Node index to exclude any versions that aren't available for the current OS / Architecture.
• Removed some unused properties and traits.

[chriskrycho]

Looks good! ⚡

[chriskrycho]

Tested on my M1 MacBook Air—

• launched native (non-Rosetta) Terminal
• created a new project
• volta pin node@15 npm@7

—it works perfectly!