Add IsAotCompatible attribute and update incompatible code

- Add a PolyFill class to InternalHelpers to allow for usage of attributes in netstandard
- Add EnumHelpers class to InternalHelpers to support a single API for different target frameworks

- Update generation of RegisterDefaultConversions to not use reflection but generate necessary bindings directly
- Update generations of Units to use EnumHelpers
- Add generic overloads where a type is passed in a method
- Annotate methods where I did not find a simple fix with RequiresDynamicCode attributes

Author: OleRoss

CodeGen/Generators/UnitsNetGen/QuantityGenerator.cs

@@ -40,6 +40,7 @@ public string Generate()
 using System.Globalization;
 using System.Linq;
 using System.Runtime.Serialization;
+using UnitsNet.InternalHelpers;
 using UnitsNet.Units;
 #if NET
 using System.Numerics;
@@ -156,7 +157,7 @@ private void GenerateStaticConstructor()
 
             Writer.WL($@"
             BaseUnit = {_unitEnumName}.{_quantity.BaseUnit};
-            Units = Enum.GetValues(typeof({_unitEnumName})).Cast<{_unitEnumName}>().ToArray();
+            Units = EnumHelpers.GetValues<{_unitEnumName}>();
             Zero = new {_quantity.Name}(0, BaseUnit);
             Info = new QuantityInfo<{_unitEnumName}>(""{_quantity.Name}"",
                 new UnitInfo<{_unitEnumName}>[]

CodeGen/Generators/UnitsNetGen/StaticQuantityGenerator.cs

@@ -130,6 +130,14 @@ internal static IEnumerable<Type> GetQuantityTypes()
             yield return typeof({quantity.Name});");
             Writer.WL(@"
         }
+
+        internal static void RegisterDefaultConversions(UnitConverter unitConverter)
+        {");
+            foreach (var quantity in _quantities)
+                Writer.WL($@"
+            {quantity.Name}.RegisterDefaultConversions(unitConverter);");
+            Writer.WL(@"
+        }
     }
 }");
             return Writer.ToString();

CodeGen/Generators/UnitsNetGen/UnitTestBaseClassGenerator.cs

@@ -181,6 +181,7 @@ public string Generate()
 using UnitsNet.Tests.Helpers;
 using UnitsNet.Tests.TestsBase;
 using UnitsNet.Units;
+using UnitsNet.InternalHelpers;
 using Xunit;
 
 // Disable build warning CS1718: Comparison made to same variable; did you mean to compare something else?
@@ -1011,7 +1012,7 @@ public void EqualsReturnsFalseOnNull()
         [Fact]
         public void HasAtLeastOneAbbreviationSpecified()
         {{
-            var units = Enum.GetValues(typeof({_unitEnumName})).Cast<{_unitEnumName}>();
+            var units = EnumHelpers.GetValues<{_unitEnumName}>();
             foreach (var unit in units)
             {{
                 var defaultAbbreviation = UnitsNetSetup.Default.UnitAbbreviations.GetDefaultAbbreviation(unit);