🏷️ adjust types to allow updating the SDK in Datadog app (#1587)

* make `startView` argument optional

* export TimeStamp from `/internal`

Since 85e732d , Records timestamp is
using the TimeStamp type. We need it to mock records in web-ui

packages/rum-core/src/boot/rumPublicApi.ts

@@ -155,7 +155,7 @@ export function makeRumPublicApi(
   }
 
   const startView: {
-    (name: string): void
+    (name?: string): void
     // (options: ViewOptions): void // uncomment when removing the feature flag
   } = monitor((options?: string) => {
     const sanitizedOptions = typeof options === 'object' ? options : { name: options }

packages/rum/src/entries/internal.ts

@@ -5,6 +5,7 @@
  * WARNING: this module is not intended for public usages, and won't follow semver for breaking
  * changes.
  */
+export type { TimeStamp } from '@datadog/browser-core'
 export { PRIVACY_ATTR_NAME, PRIVACY_ATTR_VALUE_HIDDEN, PRIVACY_CLASS_HIDDEN, NodePrivacyLevel } from '../constants'
 
 export * from '../types'