Code cleanup: Use number formatting utilities from the standard library

[mcooley]

We should avoid using the NumberFormattingUtils class in CalcManager. The standard libraries in both C# and C++ offer number-formatting functionality, and we should use that where possible.

This PR removes all use of NumberFormattingUtils from Graphing Calculator code, so the only remaining code that uses it is in unit converter. Unit converter has many other problems (see #379), so I didn't attempt to refactor it in this PR.

There are three areas that changed:

• Remove "fixed point with trimmed trailing zeros" formatting from the Graphing Calculator share output. Instead, use C#'s double.ToString(), which defaults to the general ("G") format. The notable change in behavior vs. the previous behavior is that scientific notation might be used if it enables a shorter output, although this should be rare since numbers of this magnitude are hard to input in the UI.
• Remove "fixed point with trimmed trailing zeros" formatting from the Graph Settings code. Instead, use the default format of wostringstream, which is also a "general"-type format. Again, this changes behavior so scientific notation could be used, so we also need to change the code where these numbers are parsed back to doubles to use wistringstream, which can handle the scientific notation format.
• Finally, move NumberFormattingUtils to the UnitConversionManager namespace. This indicates that it's intended for use only in the existing UnitConversionManager code and can be deleted if that code is refactored or removed.

[mcooley]

This is a low-priority cleanup PR which is not urgent, but I'd also like to get it merged before I forget all the details about how it works :) @tian-lt @hanzhang54 @guominrui can one of you review this sometime soon?

[hanzhang54]

Thanks Matt! It looks good to me. 😊

[hanzhang54]

/azp run

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