This adds support for using a local copy of an npm package.
```js
// deno.json
{
"patch": [
"../path/to/local_npm_package"
],
// required until Deno 2.3, but it will still be considered unstable
"unstable": ["npm-patch"]
}
```
1. Requires using a node_modules folder.
2. When using `"nodeModulesDir": "auto"`, it recreates the folder in the
node_modules directory on each run which will slightly increase startup
time.
3. When using the default with a package.json (`"nodeModulesDir":
"manual"`), updating the package requires running `deno install`. This
is to get the package into the node_modules directory of the current
workspace. This is necessary instead of linking because packages can
have multiple "copy packages" due to peer dep resolution.
Caveat: Specifying a local copy of an npm package or making changes to
its dependencies will purge npm packages from the lockfile. This might
cause npm resolution to resolve differently and it may end up not using
the local copy of the npm package. It's very difficult to only
invalidate resolution midway through the graph and then only rebuild
that part of the resolution, so this is just a first pass that can be
improved in the future. In practice, this probably won't be an issue for
most people.
Another limitation is this also requires the npm package name to exist
in the registry at the moment.
