feat(cdk/scrolling): Integrate Pretext Library for Precise Text Measurement in Auto-Size Virtual Scroll

### Feature Description

**Description:**

### Problem Statement

The current `AutoSizeVirtualScrollStrategy` implementation relies on `ItemSizeAverager` to estimate the size of unseen items based on historical measurements. While this approach works for many scenarios, it has several limitations:

1. **Reflow overhead**: Must render elements first before measuring, triggering expensive layout reflows
2. **Inaccurate predictions**: Averaging-based estimation can be imprecise for heterogeneous content, especially variable-height text items
3. **Performance bottlenecks**: Frequent DOM measurements during scrolling impact performance
4. **Layout shifts**: Predictive scrolling may cause visual jumps when estimated sizes differ significantly from actual sizes

### Proposed Solution

I'd like to propose integrating the **Pretext** library (https://github.com/chenglou/pretext) into the auto-size virtual scroll strategy. Pretext is a pure JavaScript/TypeScript library that provides:

- **Accurate text measurement without DOM**: Calculates text dimensions using pure arithmetic, avoiding `getBoundingClientRect` and `offsetHeight`
- **Excellent performance**: Benchmarks show `layout()` operations at ~0.09ms for 500 texts (hot path)
- **Comprehensive language support**: Handles all languages, emojis, and mixed-bidi text correctly
- **Predictive sizing**: Enables pre-rendering size calculations for virtual lists

### Implementation Ideas

The integration could work as follows:

1. **For text-heavy virtual lists**:
- When items contain primarily text content with known font/line-height configurations
- Use Pretext's `prepare()` + `layout()` API to calculate heights before rendering
- This allows the scroll strategy to know exact item sizes upfront

2. **Hybrid approach**:
- Use Pretext for text content measurement
- Fall back to current DOM measurement for non-text or complex layouts
- Combine both for maximum accuracy

3. **Performance optimization**:
- Cache `PreparedText` objects for reuse during resize events
- Only re-run `layout()` (the cheap 0.09ms operation) when container width changes

### Benefits

- **Eliminates layout reflow** for text measurement in virtual lists
- **More accurate scrolling behavior** with predictable item sizes
- **Better performance** especially for long lists with variable-height text items
- **Reduced visual jumps** during scrolling since sizes are pre-calculated
- **Support for all languages and scripts** including complex layouts

### Example Use Case
- Chat applications with varying message lengths.
- Feeds/Dashboards with dynamic text content.

### Use Case

_No response_

Start with the AutoSizeVirtualScrollStrategy and its ItemSizeAverager, then review the proposed Pretext prepare() and layout() APIs and how text-heavy items differ from complex layouts. Define the integration scope, fallback behavior, and validation needed to show accurate sizing without regressions.

Written by the indexing model from the issue text.