Fix radio field crash with nested option strings

[FloEdelmann]

When a radio field uses stringsCrossReference to reference another field whose option strings are structured as { title, description } objects (rather than flat strings), rendering the field throws:

TypeError: callback.apply is not a function

This happens because tInfo returns the raw { title, description } object in texts, and t.append then calls selection.call(object) — but D3's selection.call() expects a function.

The combo field already handles this correctly via its getLabelId helper, which checks for a .title sub-key first. The radio field was missing equivalent logic.

This issue was exposed by openstreetmap/id-tagging-schema#2268, which changes the parking_entrance field from type combo to type radio. The parking field it references via stringsCrossReference uses nested { title, description } option strings.

[FloEdelmann]

Yay, issue #12345 🥳 😄

[tordans]

This will not happen anymore after ideditor/schema-builder#281, right?

[tyrasd]

This will not happen anymore after ideditor/schema-builder#281, right?

No, this fix is still relevant also when we have pre-resolved strings: If a radio field references strings from a combo field with "nested" strings (i.e. separate title and description properties), the radio field still needs to explicitly choose the .title string instead of the simple "non-nested" string that radio fields usually have.

• We might want to document how radio fields interpret strings in the schema-builder docs: https://github.com/ideditor/schema-builder/#strings