Fix issue 1459-Add Capture Fullpage Screenshot keyword

[certainly-param]

Fixes #1459

Implements the fullpage screenshot functionality requested in issue #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.

Closes #1459

[certainly-param]

Ready for review - Implements fullpage screenshot functionality as requested in issue #1459. All tests passing, ready for maintainer review. Thanks!

[emanlove]

@certainly-param What happens when the screen size is limited to less than the full page size? Will this still capture the full size or not? I could see there being some issues here with limited screen sizes.

[aditisep1994]

I approve this pull request

[nevaspid]

We need this fix ! what's missing to approve/resolve ?

[aaltat]

I would vote against this feature and would close the PR.

1. This feature does not relay on selenium functionality. Instead it relies on different techniques for different browser vendors. This library usually does not have features which relies with functionality outside of the selenium API.
2. The quality of the code is not par with the rest of the library. There are hard coder things, code duplication and many other things that in my mind prevent merging this feature
3. Because there is lots of browser specific functionality, this would require testing with browser in the CI. This would require changing the CI workflow and accepting that cost by the maintainers. Adding single browser increase cost quite significantly.

As a workaround, if you need this feature you can copy/paste the code and make a plugin: https://github.com/robotframework/SeleniumLibrary/tree/master/docs/extending/plugin_api If you find it useful you can publish it as a Python package which everyone can use.

As a general note, being polite pays of for a long way and understanding hurry is important.