Support implicit conversion for number types

[Serg046]

public void M() {
    int a = 6;
    Test(a, "");
}
    
public void Test(double x, string y) {}

The construction above compiles to this

        IL_0000: ldc.i4.6
        IL_0001: stloc.0
        IL_0002: ldarg.0
        IL_0003: ldloc.0
        IL_0004: conv.r8
        IL_0005: ldstr ""
        IL_000a: call instance void C::Test(float64, string)

Add support for such conversions