docs: Add conditional TypeScript block to migration guide

docs/guides/migrating.md

@@ -53,6 +53,8 @@ Now `import { HookContext } from './declarations'` can be used as the context in
 
 ### Service types
 
+<LanguageBlock global-id="ts">
+
 Service types now only need the actual service class type and should no longer include the `& ServiceAddons<any>`. E.g. for the messages service like this:
 
 ```ts
@@ -64,6 +66,14 @@ declare module '../../declarations' {
 }
 ```
 
+</LanguageBlock>
+
+<LanguageBlock global-id="js">
+
+You have selected JavaScript as the language which does not have type information.
+
+</LanguageBlock>
+
 ### Configuration types
 
 A Feathers application can now also include types for the values of `app.set` and `app.get`. The configuration can also be validated and the type inferred from a [Feathers schema](../api/schema/index.md).