Add `Dispatch Event` keyword to fire DOM events on an element

@Snooz82 is already working on this.

Since Aug 6, 2026.

## Use case

Some events simply cannot be produced by real user-input keywords: application-defined custom events, `dragstart`/`dragend` on exotic drag implementations, synthetic `change`/`input` events on components that swallow real input, `deviceorientation`, and similar. Today the only escape hatch is hand-written `Evaluate JavaScript` such as `(e) => e.dispatchEvent(new Event('change'))` — which gets none of Playwright's benefits: no auto-waiting for the element to be attached, no strict-mode selector resolution, and no automatic mapping of the event type to the correct event class (`MouseEvent`, `DragEvent`, `TouchEvent`, …) with properly initialized properties.

Playwright covers this with `dispatchEvent`, available both element-scoped (locator) and page-scoped; a single selector-based keyword covers both use cases since the library addresses elements by selector anyway.

## Proposed keyword / arguments

`Dispatch Event selector event eventInit=&{EMPTY} *, timeout=None`

- `selector` — element to receive the event (strict-mode resolved, auto-waits for attachment; supports `->>` frame piercing like other element keywords).
- `event` — DOM event type, e.g. `click`, `dragstart`, `change`, or a custom event name.
- `eventInit` — dictionary passed to the event constructor (Playwright picks `DragEvent`, `MouseEvent`, etc. based on the event type and composes it accordingly).
- `timeout` — maximum wait time for the element; library timeout when omitted.

```robotframework
Dispatch Event id=source dragstart
Dispatch Event css=.widget app:refresh
&{init}= Create Dictionary bubbles=${True} cancelable=${True}
Dispatch Event id=form-field change ${init}
Get Text id=status == changed
```

## Playwright API

- [`locator.dispatchEvent`](https://playwright.dev/docs/api/class-locator#locator-dispatch-event)
- [`page.dispatchEvent`](https://playwright.dev/docs/api/class-page#page-dispatch-event) (same capability, addressed via selector — covered by the one keyword)

## Implementation notes

- New RPC in `protobuf/playwright.proto` (selector, event type, serialized eventInit, timeout/strict).
- `node/playwright-wrapper`: resolve the locator with the existing selector machinery and call `locator.dispatchEvent(event, eventInit)`.
- Python keyword in `Browser/keywords/interaction.py`, docs, atest cases including a custom event and an event carrying `eventInit` data.

## Backwards compatibility

Purely additive: a new keyword; existing `Evaluate JavaScript` workarounds keep working unchanged.