fix(ui5-illustrated-message): correct resizing on height change

[NakataCode]

Problem

The IllustratedMessage component entered an infinite re-rendering loop when placed in a height-constrained container. The resize handler conflicted between width-based and height-based calculations:

1. Width calculation selects larger illustration (SCENE)
2. Height overflow triggers smaller illustration (SPOT)
3. Re-render fires resize observer again
4. Loop repeats: SCENE → SPOT → SCENE → SPOT...

This caused visual flickering and performance issues during resizing.

Solution

1. Height-Constrained Mode

• Added _isHeightConstrained flag to lock into height-based calculation once overflow is detected
• Prevents switching back to width-based sizing
• Resets when container grows significantly (+10px)

2. Dimension-Based Cache

• Tracks dimensions per media type
• Blocks media switches if dimensions already match cached values (within 1px)
• Prevents re-rendering cycles

3. Debounced Adjustments

• Uses requestAnimationFrame cancellation to prevent multiple queued callbacks
• Ensures only one adjustment runs per frame

4. Smart Early Return

• Skips updates when calculated media matches current media

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Cypress test - to be added!

Fixes: #12673

[ui5-webcomponents-bot]

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