rust: kunit: Support KUnit tests with a user-space like syntax

This series was originally written by José Expósito, and can be found here:
https://github.com/Rust-for-Linux/linux/pull/950

Add support for writing KUnit tests in Rust. While Rust doctests are already converted to KUnit tests and run, they're really better suited for examples, rather than as first-class unit tests.

This series implements a series of direct Rust bindings for KUnit tests, as well as a new macro which allows KUnit tests to be written using a close variant of normal Rust unit test syntax. The only change required is replacing '#[cfg(test)]' with '#[kunit_tests(kunit_test_suite_name)]'

An example test would look like:

	#[kunit_tests(rust_kernel_hid_driver)]
	mod tests {
	    use super::*;
	    use crate::{c_str, driver, hid, prelude::*};
	    use core::ptr;

	    struct SimpleTestDriver;
	    impl Driver for SimpleTestDriver {
	        type Data = ();
	    }

	    #[test]
	    fn rust_test_hid_driver_adapter() {
	        let mut hid = bindings::hid_driver::default();
	        let name = c_str!("SimpleTestDriver");
	        static MODULE: ThisModule = unsafe { ThisModule::from_ptr(ptr::null_mut()) };

        	let res = unsafe {
	            <hid::Adapter<SimpleTestDriver> as driver::DriverOps>::register(&mut hid, name, &MODULE)
	        };
	        assert_eq!(res, Err(ENODEV)); // The mock returns -19
	    }
	}

Changes since the GitHub PR:
- Rebased on top of kselftest/kunit
- Add const_mut_refs feature
This may conflict with https://lore.kernel.org/lkml/[email protected]/
- Add rust/macros/kunit.rs to the KUnit MAINTAINERS entry

---
José Expósito (3):
rust: kunit: add KUnit case and suite macros
rust: macros: add macro to easily run KUnit tests
rust: kunit: allow to know if we are in a test

 MAINTAINERS          |   1 +
 rust/kernel/kunit.rs | 181 +++++++++++++++++++++++++++++++++++++++++++++++++++
 rust/kernel/lib.rs   |   1 +
 rust/macros/kunit.rs | 149 ++++++++++++++++++++++++++++++++++++++++++
 rust/macros/lib.rs   |  29 +++++++++
 5 files changed, 361 insertions(+)

---
base-commit: 64bd4641310c41a1ecf07c13c67bc0ed61045dfd
change-id: 20230720-rustbind-477964954da5

Best regards,

David Gow <[email protected]>