Additional Floating Point Precision Changes

[oleibman]

Fix #1324, which went stale many years ago, and is now re-opened. It can be considered a follow-on to PR #4479 which was installed in May. The user complains of a very small loss of precision. This can be corrected by using StringHelper::convertToString in lieu of a simple cast from float to string in two places. Style\NumberFormat\Formatter is quite straightforward. Writer\Csv is a bit more complicated. If you put a float with more than 15 digits precision in a Csv, on opening it Excel will give a pop-up, saying something inaccurate like "We've corrected this for you - is that okay?" Better to avoid that by making sure to avoid too much precision when writing to Csv.

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.