feat(aria-snapshot): add numberSubstitution option for baseline generation

[adityasingh2400]

Closes #40080.

The aria-snapshot baseline generator currently rewrites numbers and dates into \d+ regexes, which is helpful for live UIs but unwanted for tests against mocked endpoints where the values are stable. This adds a numberSubstitution: 'regex' | 'static' option (default 'regex' so existing baselines do not change) that can be set per matcher call or globally via the expect.toMatchAriaSnapshot config.

Usage:

// per call
await expect(page.locator('body')).toMatchAriaSnapshot(`...`, { numberSubstitution: 'static' });

// globally
export default defineConfig({
  expect: {
    toMatchAriaSnapshot: { numberSubstitution: 'static' },
  },
});

The option is plumbed through expressionArg on the existing to.match.aria channel, then read inside matchesExpectAriaTemplate to gate the regex-rewrite step in renderAriaTree's codegen mode.

Tests cover both modes plus the existing default behavior, including the precedence where a per-call option overrides the global config.