Fix some ambiguity issues

Author: Muximize

UnitsNet.Tests/CustomCode/MassConcentrationTests.cs

@@ -131,7 +131,7 @@ public static void ComponentMassFromMassConcentrationAndSolutionVolume(
             var massConcentration = new MassConcentration(massConcValue, massConcUnit);
             var volume = new Volume(volumeValue, volumeUnit);
 
-            Mass massComponent = massConcentration * volume;
+            Mass massComponent = (Density)massConcentration * volume;
 
             AssertEx.EqualTolerance(expectedMassValue, massComponent.As(expectedMassUnit), tolerance);
         }

UnitsNet/CustomCode/Quantities/MassConcentration.extra.cs

@@ -5,13 +5,29 @@ namespace UnitsNet
 {
     public partial struct MassConcentration
     {
+        /// <summary>
+        ///     Because Density and MassConcentration are almost the same, we can convert between them.
+        /// </summary>
+        public static implicit operator MassConcentration(Density density)
+        {
+            return From(density.ToUnit(Density.BaseUnit).Value, BaseUnit);
+        }
+
+        /// <summary>
+        ///     Because Density and MassConcentration are almost the same, we can convert between them.
+        /// </summary>
+        public static explicit operator Density(MassConcentration massConcentration)
+        {
+            return Density.From(massConcentration.ToUnit(BaseUnit).Value, Density.BaseUnit);
+        }
+        
         /// <summary>
         ///     Get <see cref="Molarity" /> from this <see cref="MassConcentration" /> using the known component <see cref="MolarMass" />.
         /// </summary>
         /// <param name="molecularWeight"></param>
         public Molarity ToMolarity(MolarMass molecularWeight)
         {
-            return this / molecularWeight;
+            return (Density)this / molecularWeight;
         }
 
         /// <summary>
@@ -21,7 +37,7 @@ public Molarity ToMolarity(MolarMass molecularWeight)
         /// <returns></returns>
         public VolumeConcentration ToVolumeConcentration(Density componentDensity)
         {
-            return this / componentDensity;
+            return VolumeConcentration.FromDecimalFractions((Density)this / componentDensity);
         }
 
         #region Static Methods

UnitsNet/CustomCode/Quantities/MassFraction.extra.cs

@@ -11,7 +11,7 @@ public partial struct MassFraction
         /// <returns>The actual mass of the component involved in this mixture</returns>
         public Mass GetComponentMass(Mass totalMass)
         {
-            return totalMass * this;
+            return totalMass * DecimalFractions;
         }
 
         /// <summary>
@@ -21,7 +21,7 @@ public Mass GetComponentMass(Mass totalMass)
         /// <returns>The total mass of the mixture</returns>
         public Mass GetTotalMass(Mass componentMass)
         {
-            return componentMass / this;
+            return componentMass / DecimalFractions;
         }
 
         #region Static Methods

UnitsNet/CustomCode/Quantities/Molarity.extra.cs

@@ -20,7 +20,7 @@ public MassConcentration ToMassConcentration(MolarMass molecularWeight)
         /// <param name="componentMass"></param>
         public VolumeConcentration ToVolumeConcentration(Density componentDensity, MolarMass componentMass)
         {
-            return this * componentMass / componentDensity;
+            return VolumeConcentration.FromDecimalFractions(this * componentMass / componentDensity);
         }
 
         #region Static Methods

UnitsNet/CustomCode/Quantities/VolumeConcentration.extra.cs

@@ -43,7 +43,7 @@ public static VolumeConcentration FromVolumes(Volume componentVolume, Volume mix
         /// <param name="componentMolarMass"></param>
         public static VolumeConcentration FromMolarity(Molarity molarity, Density componentDensity, MolarMass componentMolarMass)
         {
-            return molarity * componentMolarMass / componentDensity;
+            return FromDecimalFractions(molarity * componentMolarMass / componentDensity);
         }
 
         #endregion