fix: tolerate page errors without location

[mturac]

Fixes #41169.

When a browser reports a page error without source location metadata, normalize it to an empty location before storing and dispatching the error. This keeps both pageerror and weberror events flowing instead of crashing the driver while preserving the existing event payload shape.

The Firefox protocol type now reflects that Page.uncaughtError.location can be omitted.

Validation:

• npm run build
• node packages/playwright-test/cli.js test --config=tests/library/playwright.config.ts browsercontext-events.spec.ts -g "weberror event should tolerate missing location"
• npm run tsc -- --pretty false
• npm run eslint -- packages/playwright-core/src/server/page.ts tests/library/browsercontext-events.spec.ts
• git diff --check