Format add g final step

[berni44]

No description provided.

[dlang-bot]

Thanks for your pull request and interest in making D better, @berni44! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
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• My PR is fully covered with tests (you can see the coverage diff by visiting the details link of the codecov check)
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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	21641	minor	std.format: %g produces in rare circumstances inconsistent result

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + phobos#7853"

[thewilsonator]

Otherwise looks great.

[thewilsonator]

Note: compile time formatting reals remains unsupported.