[Feature]: contextual role-based locators (before and after)

Nobody has claimed this yet.

### 🚀 Feature Request

I don't want to drop to CSS Selectors or XPath bu use the Accessiblity Tree and search for elements before and/or after other elements.

### Example

```ts
// find an element only if it appears before another in the accessiblity tree
const searchByZipCode = page.getByRole("textbox", {
before: page.getByRole("button", { name: "Submit" }),
});

// find an element only if it appears after another in the accessiblity tree
const childInfoTable = page.getByRole("table", {
after: page.getByRole("heading", { name: "Child Info" }),
});

// find an element only if it appears between two others in the accessibility tree
const parentInfoTable = page.getByRole("table", {
after: page.getByRole("heading", { name: "Parent Info" }),
before: page.getByRole("heading", { name: "Dietary Restrictions" )),
});
```

### Motivation

A page can contain multiple matches for a selector (e.g. multiple tables) and to be less dependent on page implementations it is desirable to not use test IDs, class names, etc. but rely on queues for real users such as contextual information (e.g. preceding headings to a table where there are multiple tables on a page each with their own headings).

This is possible with CSS Selectors and XPath but not yet possible with role-based locators.

The issue names no implementation files, tests, or entry points. Start by reviewing Playwright's role-based locator API and accessibility-tree behavior, then define how before, after, and combined constraints should work and add coverage for the three example cases.

Written by the indexing model from the issue text.