New Algorithm for TRUNC, ROUNDUP, and ROUNDDOWN

[oleibman]

Fix #4113. TRUNC isn't always producing the expected result. There was a promising algorithm at https://stackoverflow.com/questions/4668628/truncate-float-numbers-with-php from user Juan. It works through Php8.3, but failed in Php8.4 (more on this later). User Savageman on the same page has a solution that needs work, but, once the work had taken place, it works on Php8.1-8.4.

The ROUNDUP and ROUNDDOWN functions were adversely affected by Php8.4, probably for the same reasons as Juan's TRUNC suggestion. I put a kludge in place for them some time ago, but I wasn't happy with it. The solution used for TRUNC here suggested a change to the ROUNDUP and ROUNDDOWN code that would no longer require the kludge. The change to those functions now works more cleanly on Php8.1-8.4.

This is:

• a bugfix
• a new feature
• refactoring
• additional unit tests

Checklist:

• Changes are covered by unit tests
  • Changes are covered by existing unit tests
  • New unit tests have been added
• Code style is respected
• Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• CHANGELOG.md contains a short summary of the change and a link to the pull request if applicable
• Documentation is updated as necessary

Why this change is needed?

Provide an explanation of why this change is needed, with links to any Issues (if appropriate).
If this is a bugfix or a new feature, and there are no existing Issues, then please also create an issue that will make it easier to track progress with this PR.