Where possible without breaking compatibility, rename "hint" to "server_id".

We're committed to mongoc_bulk_operation_get/set_hint, mongoc_cursor_get_hint. There, just explain in the docs that we really mean server_id, and rename the "hint" parameter.

Everywhere else, rename parameters and internal names from hint to server_id.

Rename mongoc_apm_command_started_get_hint, mongoc_apm_command_succeeded_get_hint, mongoc_apm_command_failed_get_hint before we release APM. Rename mongoc_client_command_simple_with_hint.