[PM-16793] port credential generator service to providers (#14071)

* introduce extension service
* deprecate legacy forwarder types
* eliminate repeat algorithm emissions
* extend logging to preference management
* align forwarder ids with vendor ids
* fix duplicate policy emissions; debugging required logger enhancements

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Co-authored-by: Daniel James Smith <2670567+djsmith85@users.noreply.github.com>

libs/tools/generator/extensions/legacy/src/forwarders.ts

@@ -0,0 +1,63 @@
+import { IntegrationId } from "@bitwarden/common/tools/integration";
+
+export type ForwarderId = IntegrationId;
+
+/** Metadata format for email forwarding services. */
+export type ForwarderMetadata = {
+  /** The unique identifier for the forwarder. */
+  id: ForwarderId;
+
+  /** The name of the service the forwarder queries. */
+  name: string;
+
+  /** Whether the forwarder is valid for self-hosted instances of Bitwarden. */
+  validForSelfHosted: boolean;
+};
+
+/** Metadata about an email forwarding service.
+ *  @remarks This is used to populate the forwarder selection list
+ *  and to identify forwarding services in error messages.
+ */
+export const Forwarders = Object.freeze({
+  /** For https://addy.io/ */
+  AddyIo: Object.freeze({
+    id: "anonaddy",
+    name: "Addy.io",
+    validForSelfHosted: true,
+  } as ForwarderMetadata),
+
+  /** For https://duckduckgo.com/email/ */
+  DuckDuckGo: Object.freeze({
+    id: "duckduckgo",
+    name: "DuckDuckGo",
+    validForSelfHosted: false,
+  } as ForwarderMetadata),
+
+  /** For https://www.fastmail.com. */
+  Fastmail: Object.freeze({
+    id: "fastmail",
+    name: "Fastmail",
+    validForSelfHosted: true,
+  } as ForwarderMetadata),
+
+  /** For https://relay.firefox.com/ */
+  FirefoxRelay: Object.freeze({
+    id: "firefoxrelay",
+    name: "Firefox Relay",
+    validForSelfHosted: false,
+  } as ForwarderMetadata),
+
+  /** For https://forwardemail.net/ */
+  ForwardEmail: Object.freeze({
+    id: "forwardemail",
+    name: "Forward Email",
+    validForSelfHosted: true,
+  } as ForwarderMetadata),
+
+  /** For https://simplelogin.io/ */
+  SimpleLogin: Object.freeze({
+    id: "simplelogin",
+    name: "SimpleLogin",
+    validForSelfHosted: true,
+  } as ForwarderMetadata),
+});