[expressions] Convert `interpreter_functional` test suite to use new unified expectSnapshot implementation.

[lukeelmers]

Currently the test/interpreter_functional suite has its own implementation of Jest-like snapshots for testing. Since #82932 has been merged there's now a unified snapshot implementation that can be used across functional test suites... we should look into replacing the existing interpreter test snapshots with the new shared ones.

[elasticmachine]

Pinging @elastic/kibana-app-services (Team:AppServices)

[ppisljar]

Thank you for contributing to this issue, however, we are closing this issue due to inactivity as part of a backlog grooming effort. If you believe this feature/bug should still be considered, please reopen with a comment.