feat: Create SubdomainExtensionBasedMapper

This is required for file backends when supporting identifiers containing subdomains.

package.json

@@ -84,6 +84,7 @@
     "@types/n3": "^1.4.4",
     "@types/node": "^14.10.2",
     "@types/pump": "^1.1.0",
+    "@types/punycode": "^2.1.0",
     "@types/rdf-js": "^4.0.0",
     "@types/sparqljs": "^3.1.0",
     "@types/streamify-array": "^1.0.0",
@@ -101,6 +102,7 @@
     "mime-types": "^2.1.27",
     "n3": "^1.8.0",
     "pump": "^3.0.0",
+    "punycode": "^2.1.1",
     "rdf-parse": "^1.7.0",
     "rdf-serialize": "^1.1.0",
     "rdf-terms": "^1.5.1",