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.