Fix --data-path command line option and remove redundant path objects/methods from Platform::

[SRSaunders]

Description

1. Restores/Implements --data-path command line option to support running from an arbitrary working directory
2. Removes rendundant path objects/methods from Platform:: - these were confusing and are no longer needed

Fixes #1056

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 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 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  • [x] I have updated the header Copyright to reflect the current year (CI build will fail if Copyright is out of date)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

Can't test on Android.

If this PR contains framework changes:

• [x] I did a full batch run using the batch command line argument to make sure all samples still work properly

Sample Checklist

Not applicable

[SRSaunders]

I am not able to add/request reviews via GitHub, so I would like to ask @tomadamatkinson and @asuessenbach to also review this. I see that 3 reviews are required for this project. Thanks.