[Core] Cover IWYU for all C++ folders

[Ziy1-Tan]

Follow up #52275 . IWYU is enabled at the example folder bazel/cpp/test in ci pipeline now and we can also run bazel build --iwyu <target> to perform iwyu anaylsis.

ray/.buildkite/cicd.rayci.yml

Lines 30 to 36 in fe0c32a

	- label: ":coral: reef: iwyu tests"
	commands:
	- bazel test --config iwyu //bazel/tests/cpp:example_test
	instance_type: small
	depends_on: oss-ci-base_build
	job_env: oss-ci-base_build
	tags: tools

It's time to cover IWYU for all C++ folders to reduce redundant headers and implicit inclusion.
Rough idea:

1. IWYU CI pipeline for a small C++ folder
2. Perform IWYU cleanup by folder and add to IWYU ci

[Ziy1-Tan]

cc @aslonnie @dentiny

[dentiny]

@Ziy1-Tan It would be nice if you could split the task into folders (example: #50586).
I should be able to find some volunteers to work on it.