Add support for interpolated strings via InterpolatedStringHandler

[alex-jitbit]

...so that appending an interpolated string like this:

sb.Append($"BLAHBLAH {integer}");

behind the scenes this should result in this (pseudo code)

ZString.AppendInterpolatedStringHandler handler = new ZString.AppendInterpolatedStringHandler(9, 1, zstringBuilder);
handler.AppendLiteral("BLAHBLAH ");
handler.AppendFormatted(value);

[github-actions[bot]]

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[universorum]

Will anyone review the PR?