Audit for rintf* and nearbyintf* intrinsics

[adpaco-aws]

Description of changes:

Restores and completes the audit for the rintf32 (rintf), rintf64 (rint), nearbyintf32 (nearbyintf) and nearbyintf64 (nearbyint) intrinsics.

Resolved issues:

Part of #1163
Fixes #1025

Call-outs:

I've tried to add comments regarding things that may be confusing. Please let me know if something's not clear and I'll add more.

Testing:

• How is this change tested? Adds 4 tests, removes 4 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.

[adpaco-aws]

Updated all tests to require diff <= 0.5 (instead of diff < 1.0) as we do for roundf* intrinsics, and renamed the roundf* test functions.