Support loading extensions with command name conflicts

[jc]

What do you want to change?

Add support for overriding command names, and automatically resolving command name conflicts.

Why?

Extensions are great but they tend to use common verbs/nouns for commands resulting in extensions not loading:

[Extension issues]
  user ~/projects/mitsuhiko-agent-stuff/pi-extensions/review.ts
    Command "/review" conflicts with /Users/james/projects/tmustier-pi-extensions/files-widget/index.ts
  auto (project) ~/projects/pi-mono/.pi/extensions/diff.ts
    Command "/diff" conflicts with /Users/james/projects/tmustier-pi-extensions/files-widget/index.ts

How? (optional)

Here are three cases we could support:

1. Overriding individual commands: tmustier-pi-extensions/files-widget/index.ts review -> review-tui
2. Prefixing all commands in an extension: tmustier-pi-extensions/files-widget/index.ts prefix files: -> files:review, files:diff, files:files.
3. Automatically disambiguating based on extension name when there is a conflict: tmustier-pi-extensions/files-widget/index.ts -> files-widget:review, files-widget:diff

Locally to unblock myself, I wired it into a new top-level setting:

  "commandMappings": [
    {
      "extensionPath": "~/projects/mitsuhiko-agent-stuff/pi-extensions/review.ts",
      "map": {
        "review": "agent-review",
        "status": "agent-status"
      }
    },
    {
      "extensionPath": "~/projects/tmustier-pi-extensions/files-widget/index.ts",
      "prefix": "files:"
    }
  ]

But you could see this being pushed into the extension specification in extensions and packages.extensions.