1. There was a lot of cloning going on with `NpmPackageInfo`. This is
now stored in an `Arc<NpmPackageInfo>` and cloning only happens on the
individual version.
2. The package cache is now cleared from memory after resolution.
3. This surfaced a bug in `deno cache` and I noticed it can be more
efficient if we have multiple root specifiers if we provide all the
specifiers as roots.
This adds support for peer dependencies in npm packages.
1. If not found higher in the tree (ancestor and ancestor siblings),
peer dependencies are resolved like a dependency similar to npm 7.
2. Optional peer dependencies are only resolved if found higher in the
tree.
3. This creates "copy packages" or duplicates of a package when a
package has different resolution due to peer dependency resolution—see
https://pnpm.io/how-peers-are-resolved. Unlike pnpm though, duplicates
of packages will have `_1`, `_2`, etc. added to the end of the package
version in the directory in order to minimize the chance of hitting the
max file path limit on Windows. This is done for both the local
"node_modules" directory and also the global npm cache. The files are
hard linked in this case to reduce hard drive space.
This is a first pass and the code is definitely more inefficient than it
could be.
Closes #15823
