The performance of FileAppender significantly decreases under JDK21

We tested FileAppender using JMH and found that compared to JDK1.8, the performance of JDK21 decreased by 30.5% (throughput decreased from 47.65 ops/ms to 33.08 ops/ms)

## configuration

1. Laptop configuration: I5-1350P CPU, 32GB DDR5 5200 RAM, and Samsung MZVL4512HBLU-00BLL 512GB SSD.
2. Log4j2 version is 2.24.3.
3. Perform three performance tests and calculate the average value.

## result

| **JDK Version** | **Score** | **gc.alloc.rate** | **gc.count** |
| --------------- | ------------ | ----------------- | ------------ |
| JDK 21.05 | 33.08 ops/ms | 635.45 MB/sec | 61.33 |
| JDK 1.8.171 | 47.65 ops/ms | 1,651.85 MB/sec | 294 |

For detailed code and configuration parameters , please refer to: [log4j2-perf-diff-jdk](https://github.com/zengzuo613/log4j2-perf-diff-jdk), Please refer to the complete test results: [jmh-result](https://github.com/zengzuo613/log4j2-perf-diff-jdk/tree/jdk1.8/jmh-result).