Fix string_build_config_mapper potentially becoming invalid due to ODR issues when restarting the runtime

[illuhad]

When no SYCL objects are around anymore, the AdaptiveCpp runtime shuts down. Because of this, defining multiple test cases as e.g. in catch2 causes runtime shutdown/restart patterns.
It seems that in this case, the string_build_config_mapper can become invalid as it might be destoryed when backends unload, and might then not be reconstructed correctly due to ODR issues.

This PR fixes this by moving kernel_configuration to the runtime, and moving the singleton definition for the name mapper to a .cpp file.

Hopefully fixes #1455
@TomMelt For me this fixes your issue. Can you confirm?

[TomMelt]

@illuhad , thanks so much for your help. The test runs successfully now.

I made sure to rebuild acpp using branch hotfix/string-build-config-mapper-lifetime, recompile the code and delete any previously cached JIT code from $HOME/.acpp/apps/

Here is the output:

$ ./a.out 
'+ptx89' is not a recognized feature for this target (ignoring feature)
'+ptx89' is not a recognized feature for this target (ignoring feature)
'+ptx89' is not a recognized feature for this target (ignoring feature)
[AdaptiveCpp Warning] kernel_cache: This application run has resulted in new binaries being JIT-compiled. This indicates that the runtime optimization process has not yet reached peak performance. You may want to run the application again until this warning no longer appears to achieve optimal performance.
'+ptx89' is not a recognized feature for this target (ignoring feature)
'+ptx89' is not a recognized feature for this target (ignoring feature)
'+ptx89' is not a recognized feature for this target (ignoring feature)
'+ptx89' is not a recognized feature for this target (ignoring feature)
'+ptx89' is not a recognized feature for this target (ignoring feature)
'+ptx89' is not a recognized feature for this target (ignoring feature)
'+ptx89' is not a recognized feature for this target (ignoring feature)
'+ptx89' is not a recognized feature for this target (ignoring feature)
'+ptx89' is not a recognized feature for this target (ignoring feature)
'+ptx89' is not a recognized feature for this target (ignoring feature)
'+ptx89' is not a recognized feature for this target (ignoring feature)
'+ptx89' is not a recognized feature for this target (ignoring feature)
'+ptx89' is not a recognized feature for this target (ignoring feature)
'+ptx89' is not a recognized feature for this target (ignoring feature)
'+ptx89' is not a recognized feature for this target (ignoring feature)
'+ptx89' is not a recognized feature for this target (ignoring feature)
'+ptx89' is not a recognized feature for this target (ignoring feature)
'+ptx89' is not a recognized feature for this target (ignoring feature)
'+ptx89' is not a recognized feature for this target (ignoring feature)
'+ptx89' is not a recognized feature for this target (ignoring feature)
'+ptx89' is not a recognized feature for this target (ignoring feature)
===============================================================================
All tests passed (2048 assertions in 2 test cases)