Editorial: queue a task in NavigationPreloadManager (#1834)
* Editorial: queue a task to resolve/reject promise in NavigationPreloadManager
The enable(), disable(), setHeaderValue(), and getState() methods resolved/rejected their promises directly from an 'in parallel' block. Wrap the promise-touching steps in a Queue a task on the responsible event loop.
Refs: #1740
* Only queue tasks for promise resolve/reject per review
Per @yoshisatoyanagisawa: keep the registration lookup, active worker null-check, and navigation-preload flag/header set/unset in the parallel block (atomic operations, safe from parallel context). Only wrap the promise-resolution and promise-rejection steps in Queue a task. Matches the pattern already used by getState().