Using ETL paths in explorers instead of variable ids doesn't work inside transform functions

[danyx23]

Description

We've recently added the ability to use ETL paths in explorers to reference indicators (rather than variable ids). This is nice because the ETL paths are stable across staging servers. One place where this translation is still missing though is inside the transform functions - here, only variable ids work.

Expected behaviour

ETL paths should be translated to variable ids inside transform functions

See https://owid.slack.com/archives/C0193RW5E2J/p1725455919852259 for more details from Lucas who ran into this