Fix: `Test.transfer_to_contract` use entrypoint

type:fixed

For LIGO developers

Introduced a bug when writing Test.transfer_to_contract in terms of Test.transfer, as the entrypoint is forgotten.

This MR adds an extra parameter to internal Test.transfer, and a new feature to get the entrypoint out of a contract.

Changelog details:

changelog/1795

+author: er433
+description: ''
+merge_request: '1795'
+title: 'Fix: `Test.transfer_to_contract` use entrypoint'
+type: fixed