constructor(options = {}) {
    this.options = options;
    this.cache = new Map();
    this.packageCache = new Map();
    this.rootPackage = null;
  }
This resolver implements a modified version of the node_modules resolution algorithm:
https://nodejs.org/api/modules.html#modules_all_together

In addition to the standard algorithm, Parcel supports:
  - All file extensions supported by Parcel.
  - Glob file paths
  - Absolute paths (e.g. /foo) resolved relative to the project root.
  - Tilde paths (e.g. ~/foo) resolved relative to the nearest module root in node_modules.
  - The package.json module, jsnext:main, and browser field as replacements for package.main.
  - The package.json browser and alias fields as an alias map within a local module.
  - The package.json alias field in the root package for global aliases across all modules.