[RTE] Emit update:interaction only when the built interaction content changes

[rtibblesbot]

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Overview

Three QTI interaction editors emit update:interaction when they mount or switch into edit mode, even though nothing has changed. AssociateInteractionEditor.vue was changed in #6113 to emit only on a real content change; the others still push a rebuilt interaction block at the parent just for being opened.

Complexity: Low
Target branch: unstable

Context

• ChoiceInteractionEditor.vue:382 — { immediate: true }, no mode gate: emits on mount in any mode.
• OrderingInteractionEditor.vue:309 — the props.mode watcher emits on entering edit mode.
• TextEntryEditor.vue:338-350 — { immediate: true }; gated on edit mode, still emits on mount.
• All three watch a computed that rebuilds a fresh object on every state change, so an edit producing identical XML still emits.
• AssociateInteractionEditor.vue is the reference shape after Add the QTI associate interaction plugin #6113.

The Change

• Each editor should emit update:interaction only in edit mode, and only when the rebuilt bodyXml / responseDeclarations differ by value from what it last emitted.
• Opening an editor, switching mode, or retyping identical content should produce no emit.

Acceptance Criteria

• Choice, ordering, and text entry editors do not emit update:interaction on mount.
• None of the three emit when mode changes without a content change.
• None of the three emit when a state change rebuilds identical bodyXml and responseDeclarations.
• Each still emits after an edit that changes the built XML.
• Specs asserting emit-on-mount are updated, and the no-emit cases are covered by new tests.

AI usage

Written by Claude Code while addressing review feedback on #6113. The reviewer asked for this emit behaviour on the associate editor; I grepped the other interaction editors for the same pattern, confirmed each line reference above by reading the code, and filed this rather than widening that PR.