This PR packages @zkat's work to enable package acquisition on the web. This is broken into 3 parts:

1. A replacement for npm that runs in the browser. Right now it's orogene -- for our purposes, a drop-in npm replacement. But it could be something much simpler and hackier if we want to avoid shipping a large WASM bundle at first. See packageManager.ts; the associated README has instructions on how to install orogene; I didn't include it in this PR yet although Kat intends for it to be vendored eventually.
2. Support for installing packages from package.json: This PR adds a second and third virtual filesystems for node_modules that, when accessed, use the npm replacement to install packages and cache them. The extension's tsserver web host changes slightly to use the third filesystem as a fallback for paths containing node_modules. This should avoid errors on imports in TS files, but will also help both TS and JS intellisense.
3. Support for installing packages via ATA: This PR adds an implementation of typescript's ATA installer host. This is only needed for JS projects, although those with package.json will mostly use (2) above. This change depends on 5.1, because the installer host interface was not public until then.

The only thing I've done to zkat's work is to merge from main and fix the extension's tsconfigs so they can correctly load WASM bundles without having to switch to ES modules. (thanks @andrewbranch for helping me with this)

As far as I can tell, the current status of this code is: working end-to-end for a demo scenario, with a variety of bugs blocking other scenarios. For example, after I got the code to build and run, when I tried to load a project from a local disk, I got errors about missing files in the virtual filesystem. My guess is that most of the bugs are minor and that there are two or three major ones lurking.

The design could probably use some work as well, but I believe it's good enough to check in and start iterating on.

Here are the remaining TODOs from the prototype PR:

• Figure out why ATA doesn't kick in unless I close a .ts file first???
• Figure out why Go To Source Definition for non-module targets isn't working
• Add localStorage (or such?) support for caching previously-loaded typings
• Figure out story with CORS, esp for private registries.
• Fix file watching to make sure stuff gets updated on package.json edits (Note: will probably need to work with Nathan on this. idk what's going on with watching in general)
• Case sensitivity control?