feat(playwright-test): introduce snapshotPathTemplate configuration

[aslushnikov]

This configuration option allows to set a string with template
values for precise control over snapshot path location.

An example of snapshotPathTemplate usage:

// playwright.config.ts
// Notice the `testDir` configuration!
export default {
  testDir: './tests',
  snapshotPathTemplate: './__screenshots__/{platform}/{projectName}/{testFilePath}/{arg}{ext}',
}

Currently supported "magic tokens" inside the snapshotPathTemplate
are:

• {testDir} - project's testDir
• {snapshotDir} - project's snapshotDir
• {platform} - process.platform
• {projectName} - Project's sanitized name
• {testFileDir} - Directories in relative path from testDir to test
  file path (e.g. page/ in the example below)
• {testFileName} - Test file name (with extension) (e.g.
  page-click.spec.ts in the example below)
• {testFilePath} - Relative path from testDir to test file path
  (e.g. page/page-click.spec.ts in the example below)
• {ext} - snapshot extension (with dots)
• {arg} - joined snapshot name parts, without extension (e.g. foo/bar/baz in the example below)
• {snapshotSuffix} - testInfo.snapshotSuffix value.

Consider the following file structure:

playwright.config.ts
tests/
└── page/
    └── page-click.spec.ts

The following page-click.spec.ts:

// page-click.spec.ts
import { test, expect } from '@playwright/test';

test('should work', async ({ page }) => {
  await expect(page).toHaveScreenshot(['foo', 'bar', 'baz.png']);
});

Fixes #7792