Increase test coverage for servlet specification compliance

Currently there are two ways of mapping request events to servlet requests. The classic way is covered by tests using `com.amazonaws.serverless.proxy.internal.testutils.AwsProxyRequestBuilder`, the new way using Spring Cloud is tested in `com.amazonaws.serverless.proxy.spring.AwsSpringHttpProcessingUtilsTests`. The latter doesn't cover all cases that were already implemented in previous years, so we'd need to transfer the tests.

Ideally we'd leverage the official TCK https://github.com/jakartaee/servlet/tree/master/tck to some extend.

比较通过 com.amazonaws.serverless.proxy.internal.testutils.AwsProxyRequestBuilder 覆盖的用例与 com.amazonaws.serverless.proxy.spring.AwsSpringHttpProcessingUtilsTests。首先运行 Spring Cloud servlet 处理测试，并找出其中缺失的已实现用例。迁移相关覆盖，然后评估 Jakarta Servlet TCK 是否能增加有用的合规性检查；完成标准是新的映射路径覆盖之前的用例且测试通过。

由索引模型根据 Issue 内容生成。