`set_error_handler` should be able to handle fatal error once

Description

Currently, fatal error can be handled, but it is not possible to do so using handler set by set_error_handler, but workaround using register_shutdown_function. This is not only too complex, but there is no guarantee such handler is/was registered as the first shutdown function.

An example is here: https://github.com/phpstan/phpstan-src/blob/1.10.50/src/Command/CommandHelper.php#L137-L154

This is a feature request to allow error handler to handle fatal error when php enters into shutdown before the 1st shutdown handler is executed.

从 issue 中描述的现有 set_error_handler 和 register_shutdown_function 行为开始，并查看链接的 phpstan 示例以了解当前的 workaround。完成的标准是：致命错误可以在第一个 shutdown handler 运行之前，通过 error handler 处理一次，而不依赖单独注册的 shutdown function。