inspector: report an error when DOM storage is unavailable

[lazerg]

DOMStorage.getDOMStorageItems falls back to reading the live Storage object when its cached map is empty, but when getWebStorage() cannot produce one it skips the fallback and still answers with Success and an empty entries array. getWebStorage() returns nothing whenever globalThis.localStorage is missing or is not an object, which is the case for any process started without --localstorage-file, so a frontend cannot tell an empty store from a store it has no access to.

It now returns a Could not read DOM storage items protocol error in that case, alongside the DOMStorage domain is not enabled error the same function already produces. This does change what a DevTools frontend sees for a process with no --localstorage-file: the localStorage panel gets an error rather than an empty table. The cached map registered through DOMStorage.registerStorage still short-circuits ahead of the check, so registering an empty map reads as an empty store.

Tests: test/parallel/test-inspector-dom-storage-unavailable.js posts DOMStorage.getDOMStorageItems without --localstorage-file; it resolves with an empty result before this change and rejects with ERR_INSPECTOR_COMMAND after.

Fixes: #65895

[nodejs-github-bot]

Review requested:

• @nodejs/inspector

[github-actions]

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