[SWF Editor] LS auto-completion for full functionRef object does not work

Some changes broke auto-completion for the full functionRef object:
 "functionRef": 🎯

This test is passing when running against `0.21.1` tag (our latest release atm) but fails on `main` branch.

Cause: After 0.21.1 the use of jsonc.getLocation() has been removed in favour of matchNodeWithLocation() that uses findNodesAtLocation(), and it's based on the AST.
jsonc.getLocation() scans the file's text, not the AST, but is not compatible with YAML.