Add `Set Page Content` keyword to set the page HTML directly

Use case

Sometimes a test needs a page with exact, known HTML — component or snippet testing, reproducing a rendering bug, or exercising a keyword against a minimal DOM — without standing up a web server or writing a temporary file and navigating to a file:// URL (the current clumsy workaround). Playwright supports this directly with page.setContent, but the library does not expose it.

Proposed keyword / arguments

Set Page Content html *, wait_until=load timeout=None

• html — the HTML markup to assign to the page (replaces the whole document).
• wait_until — load state to wait for, same enum as Go To / Reload (load, domcontentloaded, networkidle, commit); default load.
• timeout — maximum wait time (Robot Framework time format); falls back to the library timeout when omitted.

New Page
Set Page Content    <h1>Hello</h1><button id="go" onclick="this.textContent='clicked'">Go</button>
Get Text    h1    ==    Hello
Click    id=go
Get Text    id=go    ==    clicked

Set Page Content    ${LONG_SNIPPET}    wait_until=domcontentloaded    timeout=5s

Playwright API

page.setContent

Implementation notes

• New RPC in protobuf/playwright.proto (html, waitUntil, timeout).
• Trivial pass-through in node/playwright-wrapper on the active page.
• Python keyword (fits Browser/keywords/playwright_state.py or the getters/content module), docs, atest with a subsequent interaction/assertion on the injected content.

Backwards compatibility

Purely additive: a new keyword; no changes to existing keywords.

Start with the related Go To and Reload RPC definitions in protobuf/playwright.proto, then inspect node/playwright-wrapper and the Python keyword modules suggested in the issue. Add an atest that injects HTML and performs a subsequent interaction and assertion, update the documentation, and verify wait_until and timeout behavior against the described Playwright API.