Rewrite `sysconfig.get_config_vars` data generation to receive clearly-defined inputs

Feature or enhancement

Proposal:

Right now, some of the data is calculated during import, then we use that to calculate more data when building the sysconfig.get_config_vars cache. It would be good to transform all of this into a clearly defined algorithm, where we the data is generated based on a set of inputs, making it easier to generate data when cross-compiling, and allowing us to generate data for a specific environment (eg. source builds, vs installed build). This would have helped mitigate issues such as GH-127429, GH-128055, and GH-126789.

Additionally, this also gives us the opportunity to split the data into two sets: the minimum needed to evaluate the install scheme paths, and the non-critical additional data we expose in sysconfig.get_config_vars. This would help with the bootstrapping issue in python -m sysconfig --generate-posix-vars.

https://github.com/python/cpython/blob/f802c8bf872ab882d3056675acc79c950fe5b93c/Lib/sysconfig/__main__.py#L206-L221

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

No response

Inizia da Lib/sysconfig/main.py, in particolare dalle righe collegate 206–221 e dal flusso python -m sysconfig --generate-posix-vars. Traccia il modo in cui i dati di configurazione vengono calcolati durante l’importazione e la generazione della cache. Il lavoro è completato quando l’algoritmo di generazione dei dati ha input chiaramente definiti, supporta ambienti distinti come la compilazione incrociata e le build installate e separa i dati dello schema di installazione dalle variabili aggiuntive esposte.