optimize the directory structure of executor package

[XuHuaiyu]

Enhancement

There are too many .go files in the package executor, we need to split the files into multiple subdirectories.

[tisonkun]

I propose to address this issue along with #26854 since almost functions relate with integration_test.go. Decoupling logics also requests rearrange tests, migration can be done on the fly. Be sure that we refactor code instead of making non-trivial changes.

[hawkingrei]

Although migrating test-infra to testify have completed, We find we can run test cases more faster and stable in the Bazel if the executor split the files into multiple subdirectories. I hope this enhancement can continue to do.

[Zheaoli]

Maybe I can make a try to split the directory(