refactor(core): document setComponentScope to provide context (#39662)

`setComponentScope` was previously undocumented. This commit adds a short
explanation of what the function does, and adds a link to a doc which
explains issues with cycles in more detail.

PR Close #39662

packages/core/src/render3/definition.ts

@@ -352,6 +352,12 @@ export function ɵɵdefineComponent<T>(componentDefinition: {
 }
 
 /**
+ * Generated next to NgModules to monkey-patch directive and pipe references onto a component's
+ * definition, when generating a direct reference in the component file would otherwise create an
+ * import cycle.
+ *
+ * See [this explanation](https://hackmd.io/Odw80D0pR6yfsOjg_7XCJg?view) for more details.
+ *
  * @codeGenApi
  */
 export function ɵɵsetComponentScope(