new: Add new executables system.

[milesj]

Historically we only had shims which was easy to maintain, but in v0.20 we also added binary symlinks alongside shims, which complicated things. There are a few issues with the current system:

• Global and local shims are confusing, maybe remove local?
• The "primary" binary to execute is a bit abstracted.
• Secondary shims are not created as symlinks in ~/.proto/bins.
  • For example, node-gyp, npx don't exist as real binaries.
  • On Windows, only .exe files are symlinked.
• Some tools required a parent tool to execute (.js requires node).
• Locating shims/bins/etc are split across many WASM functions.
• Other minor devx issues.

To remedy this, I'm attempting the following.

• All bin/shim/global logic is now powered by 1 WASM function, locate_executables.
  • Removes locate_bins and create_shims.
• Shims and bins are a 1:1 when configured, but create the 2 types of files. This ensures all shims have a sibling bin symlink.
• Local shims probably going away.
• Tools that require a parent going away (this is really only a Node.js problem).