added 2 commits

Implements the fullpage screenshot functionality requested in issue robotframework#1459.
The keyword captures the entire page content by temporarily resizing
the browser window to show the full page height, taking the screenshot,
and then restoring the original window size.

Features:
- Works with all existing screenshot options (EMBED, BASE64, custom filenames)
- Supports {index} placeholder for unique filenames
- Includes comprehensive unit and acceptance tests
- Follows same patterns as existing screenshot keywords

This is useful for capturing long pages that require scrolling to see
all content, especially helpful for debugging test failures.

…tive support

- Add Chrome DevTools Protocol (CDP) method for Chrome/Edge browsers
  Works in both headless and non-headless mode without screen size limits
- Add Firefox native full-page screenshot support
- Implement browser detection and capability checking
- Use strategy pattern with automatic fallback to window resize method
- Window resize method validates actual dimensions and warns on limitations
- Update documentation to describe the three screenshot strategies
- Resolves screen size limitation concerns in non-headless mode