Update tests & docs for new atomic intrinsics without ordering restrictions

[adpaco-aws]

Description of changes:

Restrictions on memory orderings for atomic compare-exchange intrinsics were lifted about a month ago (see #1340 for more details).

These new orderings were already supported, but not tested. This PR updates the corresponding tests, and updates the intrinsics table including all changes in #1340 as well.

Resolved issues:

Resolves #1344

Call-outs:

No changes to the tests for the stable versions of these intrinsics (i.e., compare_exchange) have been made because the compiler throws errors such as:

error: `compare_exchange`'s success ordering must be at least as strong as its failure ordering
  --> main.rs:56:46
   |
56 |     assert!(a3.compare_exchange(true, false, Ordering::AcqRel, Ordering::SeqCst) == Ok(true));
   |                                              ^^^^^^^^^^^^^^^^  ---------------- `SeqCst` failure ordering
   |                                              |
   |                                              `AcqRel` success ordering
   |                                              help: consider using `SeqCst` success ordering instead
   |
   = note: `#[deny(invalid_atomic_ordering)]` on by default

Testing:

• How is this change tested? Existing regression and adding more cases in related tests.

• Is this a refactor change? No.

Checklist

• Each commit message has a non-empty body, explaining why the change was made
• Methods or procedures are documented
• Regression or unit tests are included, or existing tests cover the modified code
• My PR is restricted to a single feature or bugfix

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.