fix: ignore imported data when querying goals with custom props

[ukutaht]

Changes

Fixes APP-217

Goals with custom props are not considered in the imported data query logic. Filtering or breaking down by such a goal on a site with imported data either:

• crashes — the goal filter emits meta.value[indexOf(meta.key, ...)] conditions against imported_custom_events, which has no meta columns → Ch.Error: UNKNOWN_IDENTIFIER, or
• over-counts — the event:goal breakdown matches imported rows by event name / page path only, attributing all imported events to a prop-restricted goal

Changes

• Imported.Base: skip imported data (with the standard unsupported_query warning) when any goal matching a top-level filter has custom props. Applied to all three table-decision paths, mirroring the existing scroll-goal handling.
• Stats.Goals.goal_join_data/1: emit "" into types and event_names_imports (consumed only by the imported merge) for custom-props goals, so the unfiltered goal breakdown no longer counts imported rows toward them — other goals in the breakdown keep their imported data.

[zoldar]

I'd consider creating a separate function like goal_join_imported_data and return only fields that are relevant in each respective context. As is, this is turning very hairball-like.

[zoldar]

Provided we split the logic, wouldn't it make more sense to filter out the custom prop goals right at the start?