Value Relation: collapsed field shows wrong text when lookup table is shared across filtered lists

[xkello]

Summary

Value Relation fields with a FilterExpression (e.g. "category" = 'drain_type' on a lookup table that stores multiple pick-lists sharing key values across categories) show the correct filtered list in the picker drawer, but the collapsed field can display the label from the wrong category when a key value collides across categories.

Example

Field "Drain Type", key value_int = 0, filter "category" = 'drain_type'. Drawer correctly shows/highlights "unknown". Collapsed field shows "accessible" instead - the label for value_int = 0 under a different category.

Root cause

Two code paths resolve Value Relation data; only one applies FilterExpression:

• ValueRelationFeaturesModel (drawer/picker list) - applies the filter. Correct.
• ValueRelationController::lookupDisplayTextOnValueChanged() in app/valuerelationcontroller.cpp (collapsed-field text, used on initial load and every value change) - queries key IN (...) against the whole lookup table with no filter and no ordering, so a key that exists under multiple categories can resolve to the wrong row.

The sibling method lookupDisplayTextOnHotreload() (used for cascading fields) already applies the filter correctly - it's only the plain value-changed path that's missing it.

Fix

Pass the current feature and apply the configured filter in lookupDisplayTextOnValueChanged(), same as lookupDisplayTextOnHotreload() already does:

• app/valuerelationcontroller.h / .cpp - add a feature parameter to lookupDisplayTextOnValueChanged() and pass useFilterExpression = !mFilterExpression.isEmpty() into lookupDisplayTextAsync().
• app/qml/form/editors/MMFormValueRelationEditor.qml - pass root._fieldController.featureLayerPair.feature at the lookupDisplayTextOnValueChanged() call site.

Behavior change

If a stored key no longer satisfies its FilterExpression, the collapsed field will now clear/invalidate the selection instead of showing the raw key as fallback text (matches existing hot-reload behavior). Fields without a FilterExpression are unaffected.

Test coverage

Extend TestFormEditors::testValueRelationControllerLookup in app/test/testformeditors.cpp with a lookup key that collides across two filter partitions, asserting the label resolved matches the active filter/form context, not the first unfiltered row.