Fix numeric formatting patterns by unwrapping scalar values

[sisve]

This fixes #3134 where numeric formatting pattern does not work.

The old behavior sends ScalarValue objects to String.Format, which .NET knows nothing about. By unwrapping ScalarValue's into their primitive values we get support for formatting patterns related to Int32 and Double, the only two subclasses of ScalarValue.

Related:

• https://learn.microsoft.com/en-us/dotnet/standard/base-types/standard-numeric-format-strings
• https://learn.microsoft.com/en-us/dotnet/standard/base-types/custom-numeric-format-strings

Before:

    print "{0:0.0}":format(13.37).
    > prints "13.37"

After:

    print "{0:0.0}":format(13.37).
    > prints "13.4"