Fix for graphics pipeline library sample (set required flags for fragment shader output pipeline library)

[SaschaWillems]

Description

Recent validation layers added additional validation for the graphics pipeline library, and the sample for this extension now triggers a validation message due to a missing flag. This PR sets this missing flags for the fragment shader output part of the pipeline library and cleans up validation. I also added clean up for the fragment shader pipelines that were created at runtime.

General Checklist:

Please ensure the following points are checked:

• [x] My code follows the coding style
• [x] I have reviewed file licenses
• [x] I have updated the header Copyright to reflect the current year (CI build will fail if Copyright is out of date)
• [x] I have commented any added functions (in line with Doxygen)
• [x] 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 build on Windows, Linux, macOS and Android. Otherwise I have documented any exceptions
• [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