Fix tostring handling code to deal with ToString("N0") with doubles and floats

[josesimoes]

Details about Problem

nanoFramework area: interpreter

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Description

Investigate probable bug in Number.ToString() native handlers: Library_corlib_native_System_Number::Format_F() Library_corlib_native_System_Number::Format_N() or in DoPrintfOnDataType() which calls nanoprintf code, so it can properly output "Nx" and "Fx" formats as described in #1650.