refactor(grids): restore setImmediate for export performance

[Copilot]

The yieldingLoop utility used in grid exporters was changed from setImmediate to setTimeout(0), causing ~400x performance degradation (986ms vs 2.4ms in benchmarks) for large dataset exports.

Changes

• Restored setImmediate.ts: Added the core-js implementation to projects/igniteui-angular/grids/core/src/ to provide efficient message queue scheduling
• Updated yielding-loop.ts: Reverted from setTimeout(chunk, 0) to setImmediate(chunk) for chunk scheduling

// Before (slow macrotask queue)
if (i < count) {
    setTimeout(chunk, 0);
}

// After (fast message queue)
if (i < count) {
    setImmediate(chunk);
}

This restores the original performance characteristics for CSV/Excel exports with large row counts.

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