feat: More ways to specify R path

[gadenbuie]

Fixes #61

Adds support for consulting the IDE for the preferred R runtime in two ways:

1. In Positron, we now consult the preffered runtime, i.e. the runtime selected by the user for the project. The extension will follow the prefferred runtime version on launch, meaning that if you launch the app with R 4.4, change to R 4.2, and relaunch the app, the second launch will use R 4.2.

2. In VS Code, the R Debugger extension includes r.rpath.{windows,mac,linux} settings. We also consult this setting. Note that the R Debugger extension should not be used in Positron. We don't skip this check if in Positron (maybe you're syncing settings?), though.

The R Path consultation order is now:

1. Positron
2. r.rpath.{windows,mac,linux} setting
3. $PATH
4. Windows registry

[jcheng5]

Just out of curiosity, not asking for a change... Is this all equivalent to globalThis.acquirePositronApi?()? (Other than you're gracefully dealing with globalThis not being an object and acquirePositronApi not being a function, both of which seem unlikely?)

[gadenbuie]

You mean globalThis?.acquirePositronApi(), right? Then yes, it's equivalent if overly cautious. I'm happy to switch to the cleaner syntax.

[jcheng5]

Hmmm, I don't think that's right... I think globalThis?. checks for globalThis being null/undefined but not acquirePositronApi. It looks to me like ?() is not a thing, I think maybe the original is best.

Or

const apa = globalThis?.acquirePositronApi;
return apa ? apa() : undefined;

Or

if (typeof acquirePositronApi === "function") {
  return acquirePositronApi();
}

(Bikeshedding so hard right now... sorry... 😬)

[jcheng5]

Or

globalThis?.acquirePositronApi?.call(globalThis)

(Alright I'm done, I promise!)

[gadenbuie]

I don't think that's right... I think globalThis?. checks for globalThis being null/undefined but not acquirePositronApi

Oh yeah, that's right. I think this is pretty succinct and brings in the right ideas:

function getPositronAPI(): undefined | any {
    if (typeof globalThis?.acquirePositronApi !== "function") { return; }

    return globalThis.acquirePositronApi();
}

[jcheng5]

Other than the one type tweak, LGTM!