Auto enable vkb enable portability

[gpx1000]

Description

Attempt to make the Framework requirement of enabling the Portability extension if on an OSX device and running Vulkan greater than or equal to 1.3 (when the Portability extension is introduced). Without this, the moltenvk instance wont be detected in instance creation. Please check instance.cpp for details.

Fixes #476

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• [x] I have updated the header Copyright to reflect the current year (CI build will fail if Copyright is out of date)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

Sample Checklist

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

• [x] I have tested the sample on at least one compliant Vulkan implementation
• [x] If the sample is vendor-specific, I have tagged it appropriately
• [x] I have stated on what implementation the sample has been tested so that others can test on different implementations and platforms
• [x] Any dependent assets have been merged and published in downstream modules
• [x] For new samples, I have added a paragraph with a summary to the appropriate chapter in the samples readme