* Look at getting half to work on vk.

* Alter half test so can always produce consistent test results.

* First pass working half on vk.

* Improve comments for vulkan extensions around half.

* Upgraded vulkan headers to v1.1.103

https://github.com/KhronosGroup/Vulkan-Headers

* * Add getFeatures on Render interface
* Vulkan renderer determines at startup if it can support half
* Parse render-features on render-test

* Small changes to half-calc.slang test.

* Structured buffer half access works as expected for Vk, but isn't for dx12, so disable for now.

* Require the half feature for renderers for the half-structured-buffer.slang test.

* * Added ToolReturnCode to be more rigerous about how a return code is passed back from a tool
* Added support for a tool being able to pass back an 'ignored' result.
* Used enum codes to indicate meanings
* Made spawnAndWait return a ToolReturnCode

* Ignore tests that don't have required render-feature

* Fix macro line continuation usage.

* Check dx12 has half support.

* Checking for half on dx12 - if CheckFeatureSupport fails, don't fail renderer initialization.

* Fix typo.