Enable swiftshader on Windows

Currently the windows bot do not run the tests under swiftshader due to not finding the layers.

Setup the build.bat script to correctly find the layers and run the tests under swiftshader.

```
cmake -GNinja -DCMAKE_BUILD_TYPE=%BUILD_TYPE% -DCMAKE_C_COMPILER=cl.exe -DCMAKE_CXX_COMPILER=cl.exe -DAMBER_USE_LOCAL_VULKAN=1 -DAMBER_ENABLE_SWIFTSHADER=1 ..
```

```
echo "%DATE% %TIME%: Starting integration tests.."
set VK_LAYER_PATH=%SRC%\build\third_party\vulkan-validationlayers\layers
set VK_ICD_FILENAMES=%SRC%\build\Windows\vk_swiftshader_icd.json
cd %SRC%
python tests\run_tests.py --test-prog-path=%SRC%\build\amber.exe --use-swiftshader
echo "%DATE% %TIME%: integration tests completed."
```