Testing framework: make type-checking run over aggregated program

Merged E. Rivas requested to merge er433/fix/build_context into dev

When running the testing framework, files are type-checked one by one. This contrasts with compile contract, where all the files are aggregated at ast_core level and then type-checked once. The situation makes loading contracts in the testing framework slower than it could be (@melwyn95 reported such a case in #ligo-test).

This MR fixes the issue by making the testing framework use the same function as compile contract.

  • has a changelog entry
Edited by E. Rivas