Add `Set Storage State` keyword and `indexedDB=`/`credentials=` arguments on `Save Storage State`

[Snooz82]

Use case

Save Storage State already lets users snapshot an authenticated session (cookies + local storage) and reuse it via New Context storageState=.... Two pieces of the storage-state story are still missing:

1. Restoring state into an already-running context. Today the only way to switch the logged-in user is to close the current context and create a new one with storageState= — which throws away all open pages, their navigation state, registered promises, console logs, etc. Playwright 1.59 added browserContext.setStorageState(), which clears and re-seeds the current context's storage in place. A Set Storage State keyword lets a suite log in as user A, act, then swap to user B mid-context without rebuilding anything.

2. Saving the full modern auth state. Many apps (notably Firebase/Firestore-based ones) keep their auth tokens in IndexedDB, and passkey/WebAuthn credentials live in the credential store — neither is captured by the current Save Storage State, so the record-once-log-in-forever pattern silently fails for those apps. Playwright's storageState() accepts indexedDB and credentials flags to include them; there is no workaround today.

Both halves belong to one story: what Save Storage State can capture, Set Storage State (and New Context storageState=) can restore.

Proposed keyword / arguments

New keyword:

• Set Storage State path — clears the current context's cookies/storage and re-seeds them from a state file previously produced by Save Storage State.

Extended keyword (new named-only arguments, defaults preserve current output):

• Save Storage State *, indexedDB=False credentials=False

*** Test Cases ***
Reuse Firebase Login Across Users
    New Context
    New Page    ${LOGIN_URL}
    Log In As    userA
    ${state_a}=    Save Storage State    indexedDB=True
    Log Out
    Log In As    userB
    ${state_b}=    Save Storage State    indexedDB=True

    # Later, switch users without recreating the context
    Set Storage State    ${state_a}
    Reload
    Get Text    id=current-user    ==    userA
    Set Storage State    ${state_b}
    Reload
    Get Text    id=current-user    ==    userB

Playwright API

• browserContext.setStorageState (Playwright 1.59)
• browserContext.storageState — indexedDB and credentials options

Implementation notes

• protobuf/playwright.proto: new RPC for SetStorageState (path in request); extend the existing SaveStorageState request with the two boolean flags.
• node/playwright-wrapper: call context.setStorageState({path}); pass indexedDB/credentials through to context.storageState().
• Browser/keywords/playwright_state.py: new set_storage_state keyword; two new named-only args on save_storage_state (which today takes no arguments and writes to ${OUTPUTDIR}/browser/state).
• Docs + atest: round-trip test — save with indexedDB=True, mutate storage, Set Storage State, assert restored values.

Backwards compatibility

Fully additive: Set Storage State is a new keyword, and the new Save Storage State arguments are named-only booleans defaulting to False, matching Playwright's defaults and the keyword's current output exactly.