Make Adapter & Persister backwards compatible for implementors

The replacement of the static `name` getter for `Adapter` and
`Persister` in Netflix#310 broke custom implementations of these classes
because `id` needed to be overridden. To retain backwards compatibility
we remove the requirement for `id` to be overridden. Instead we delegate
to `name` by default. This does not affect the in-tree implementations.

packages/@pollyjs/adapter/src/index.js

@@ -23,11 +23,16 @@ export default class Adapter {
     return 'adapter';
   }
 
-  /* eslint-disable-next-line getter-return */
   static get id() {
-    assert('Must override the static `id` getter.');
+    return this.name;
   }
 
+  /* eslint-disable-next-line getter-return */
+  static get name() {
+    assert('Must override the static `name` getter.');
+  }
+
+
   get defaultOptions() {
     return {};
   }

packages/@pollyjs/persister/src/index.js

@@ -17,9 +17,14 @@ export default class Persister {
     return 'persister';
   }
 
-  /* eslint-disable-next-line getter-return */
   static get id() {
-    assert('Must override the static `id` getter.');
+    return this.name;
+  }
+
+  // NOTE: deprecated in 4.1.0. Remove in 5.0.0
+  /* eslint-disable-next-line getter-return */
+  static get name() {
+    assert('Must override the static `name` getter.');
   }
 
   get defaultOptions() {