Fix screenshot

[yknishidate]

Description

I have resolved the issue where screenshots were not functioning in samples inheriting from ApiVulkanSample by calling the overridden VulkanSample::input_event() instead of Application::input_event(). I tested on Windows.

General Checklist:

Please ensure the following points are checked:

• [x] My code follows the coding style
• [x] I have reviewed file licenses
• [ ] I have commented any added functions (in line with Doxygen)
• [ ] I have commented any code that could be hard to understand
• [x] My changes do not add any new compiler warnings
• [x] My changes do not add any new validation layer errors or warnings
• [x] I have used existing framework/helper functions where possible
• [x] My changes do not add any regressions
• [x] I have tested every sample to ensure everything runs correctly

• [x] This PR describes the scope and expected impact of the changes I am making

  Note: The Samples CI runs a number of checks including:

  • [x] I have updated the header Copyright to reflect the current year (CI build will fail if Copyright is out of date)
  • [x] My changes build on Windows, Linux, macOS and Android. Otherwise I have documented any exceptions

Sample Checklist

If your PR contains a new or modified sample, these further checks must be carried out in addition to the General Checklist:

• [ ] I have tested the sample on at least one compliant Vulkan implementation
• [ ] If the sample is vendor-specific, I have tagged it appropriately
• [ ] I have stated on what implementation the sample has been tested so that others can test on different implementations and platforms
• [ ] Any dependent assets have been merged and published in downstream modules
• [ ] For new samples, I have added a paragraph with a summary to the appropriate chapter in the samples readme
• [ ] For new samples, I have added a tutorial README.md file to guide users through what they need to know to implement code using this feature. For example, see conditional_rendering
• [ ] For new samples, I have added a link to the Antora navigation so that the sample will be listed at the Vulkan documentation site