add docstrings to Mechanism type

Author: lobsterkatie

packages/types/src/mechanism.ts

@@ -1,9 +1,32 @@
-/** JSDoc */
+/**
+ * Metadata about a captured exception, intended to provide a hint as to the means by which it was captured.
+ */
 export interface Mechanism {
+  /**
+   * For now, restricted to `onerror`, `onunhandledrejection` (both obvious), `instrument` (the result of
+   * auto-instrumentation), and `generic` (everything else). Converted to a tag on ingest.
+   */
   type: string;
+
+  /**
+   * In theory, whether or not the exception has been handled by the user. In practice, whether or not we see it before
+   * it hits the global error/rejection handlers, whether through explicit handling by the user or auto instrumentation.
+   * Converted to a tag on ingest and used in various ways in the UI.
+   */
   handled: boolean;
+
+  /**
+   * Arbitrary data to be associated with the mechanism (for example, errors coming from event handlers include the
+   * handler name and the event target. Will show up in the UI directly above the stacktrace.
+   */
   data?: {
     [key: string]: string | boolean;
   };
+
+  /**
+   * True when `captureException` is called with anything other than an instance of `Error` (or, in the case of browser,
+   * an instance of `ErrorEvent`, `DOMError`, or `DOMException`). causing us to create a synthetic error in an attempt
+   * to recreate the stacktrace.
+   */
   synthetic?: boolean;
 }