Opening headers with a configuration provider randomly uses an invalid header config instead of the valid source config

[sean-mcmanus]

It seems based on timing. I repro it on Windows randomly, but not on Mac.

This also requires that the header file be referenced in the CMakeList.txt.

[sean-mcmanus]

I have a fix for the CMake Tools side at microsoft/vscode-cmake-tools#4655 , but as mentioned in the description we can still do another fix on the cpptools side as well.