Consolidate Tools into a single Binary

[charlespierce]

Info

• Currently, we are building separate binary packages for each of the core tools that we support (node, npm, npx, yarn), as well as for launchbin and launchscript.
• Each of these binaries includes most of the core of the Notion functionality, so they are fairly redundant with each other.
• As a result of including so many redundant binaries, the installer is quite large (~65 MB on Unix currently)
• We can save installer space as well as make Notion more adaptable to new tools going forward by consolidating these into a single executable.

Changes

• Updated the Tool trait and implementations to support receiving the command-line arguments as inputs, instead of getting them internally.
• Updated Tool::exec to return a result, instead of exiting.
• Added execute_tool function that parses the command-line arguments to determine which tool should be executed, then passes control over to that tool.
• Removed redundant binaries in favor of a single shim binary.
• Updated Unix installer to create symlinks to the shim binary named node, npm, npx, and yarn.
• Updated Unix installer to handle the case of existing shims, by updating the symlink to point to shim instead of launchbin.
• Refactored error display to reduce the duplication of if err.is_user_friendly() blocks.

Notes

• Windows installer work wasn't tackled here. If Fix Windows Shim Issues and Add Full Windows Installer #268 is merged first then I will update this to include Windows support, if this is merged first I will update that one.
• After this update, the Unix installer is ~21.5 MB, so it's roughly one-third the size.

[chriskrycho]

This is a fantastic simplification and cleanup. I find it way easier to follow this way. None of the things I noticed here require changing, so I'm giving this a 👍.

[chriskrycho]

The explanatory comment you added here is great!

[dherman]

This is a nice improvement! Love when the "-" count exceeds the "+" count :D