objectui: the two selectFirst gate hints join controlling-field names with hardcoded separators — and with two DIFFERENT ones #5432

Observation-class finding, noticed while fixing objectstack#5407. Nothing a user hits today with any urgency — it needs a field gated on two or more controlling fields, which is rare — so it carries finding and no pm:queue. Recording it because #5407 has just established the mechanism that fixes it.

#5407 item 4 established that a list separator is a locale property, and added validation.formInvalidJoiner (per-pack: ", " for Latin scripts and Korean, "、" for zh/ja, U+060C + space for Arabic) after measuring Intl.ListFormat and finding its output unusable for a truncated list.

Two other sites join user-visible names with a hardcoded separator, and they do not even agree with each other:

Both fill the {{fields}} slot of what is deliberately one shared sentence — the form renderer's own comment says the two callers exist so "the gate can never read differently depending on which side produced it" — yet a field gated on two parents reads Select Account, Owner first from the lookup and 请先选择Account / Owner from the select. Under zh/ja both separators are wrong for the script on top of that.

Suggested fix

Reuse the mechanism #5407 added rather than inventing a second one: either read validation.formInvalidJoiner at both sites, or (if the gate hint wants its own punctuation) add one fields.gateJoiner key across the ten packs. Either way it has to be one key read by both callers — two keys would recreate the divergence the shared sentence exists to prevent.

Note for the implementer: LookupField receives the labels through the dependsOnLabels prop #5407 added, so the joining happens in dependsOnFieldsText there; the form's copy is in the gatedHint memo.