Config provider API to provide all configurations upfront (as well as indicate which sources are 'active').

This is based on the discussion here: https://github.com/microsoft/vscode-cmake-tools/issues/1875

Ultimately, Unification may require that we modify how custom configuration providers work, so all configurations are provided up front. Configurations for all files are needed by EdgeSystem to build the include graph (amoung other reasons). Regarding https://github.com/microsoft/vscode-cmake-tools/issues/1875 , included in those configurations could be an indication of which project (build target) is currently active. Source selection for header files could use that information to prefer sources from the current active configuration.

Leggi la discussione collegata di vscode-cmake-tools e l'API esistente dei provider di configurazione personalizzati. Determina come devono essere rappresentate le configurazioni per tutti i file e i metadati del progetto attivo; il lavoro è completato quando esiste un contratto API concordato che supporta i dati di configurazione forniti in anticipo e la selezione della sorgente attiva.