Supports package names that aren't all lowercase.
This stores the package with a leading underscore (since that's not
allowed in npm's registry and no package exists with a leading
underscore) then base32 encoded (A-Z0-9) so it can be lowercased and
avoid collisions.
Global cache dir:
```
$DENO_DIR/npm/registry.npmjs.org/_{base32_encode(package_name).to_lowercase()}/{version}
```
node_modules dir `.deno` folder:
```
node_modules/.deno/_{base32_encode(package_name).to_lowercase()}@{version}/node_modules/<package-name>
```
Within node_modules folder:
```
node_modules/<package-name>
```
So, direct childs of the node_modules folder can have collisions between
packages like `JSON` vs `json`, but this is already something npm itself
doesn't handle well. Plus, Deno doesn't actually ever resolve to the
`node_modules/<package-name>` folder, but just has that for
compatibility. Additionally, packages in the `.deno` dir could have
collissions if they have multiple dependencies that only differ in
casing or a dependency that has different casing, but if someone is
doing that then they're already going to have trouble with npm and they
are asking for trouble in general.
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
