- Generalizes the npm version code (ex. `NpmVersion` -> `Version`,
`NpmVersionReq` -> `VersionReq`). This is a slow refactor towards
extracting out this code for deno specifiers and better usage in
deno_graph.
- Removes `SpecifierVersionReq`. Consolidates `NpmVersionReq` and
`SpecifierVersionReq` to just `VersionReq`
- Removes `NpmVersionMatcher`. This now just looks at `VersionReq`.
- Paves the way to allow us to create `NpmPackageReference`'s from a
package.json's dependencies/dev dependencies
(`VersionReq::parse_from_npm`).
