Core - Fix color gradient and utility bugs found by the tests (#914)

* Profile adaption - Fix arrow keys section including Page Down

- The arrow keys keyboard section now starts at Arrow Up instead of the key before it (Page Down)
- Updated the keyboard section test to expect only the four arrow keys

* Color quantizer - Let fully saturated colors be vibrant and grays be muted

- The saturation limits of the color types are now inclusive, so 100% saturated colors count as vibrant and 0% saturated colors count as muted
- The lightness limits stay exclusive so pure black and white are still left out
- Updated the quantizer tests to match

* Color gradients - Fix stop placement, seamless toggling and list events

- Stops on an occupied position now move down 0.001 instead of 0.002 (rounding error in the distance check)
- Flip, rotate, spread and interpolate move all stops together, so a stop can take a position another stop is leaving
- Spreading or randomizing a single stop puts it at 0 instead of NaN
- ToggleSeamless does nothing on an empty gradient and caps stretched stops at 1 instead of 100
- RemoveAt reports the removed stop and its index
- Insert links the stop like Add does and raises the add before the move
- Remove, RemoveAt, Clear and replacing a stop through the indexer unlink and stop listening to the actual removed stop
- Copying from a list of stops sorts them by position
- Obsolete GetPositionsArray no longer skips the seamless positions, obsolete GetColor picks the right colors after a repeat
- Updated the gradient tests to match

* Core - Fix small color, enum, string and type utility bugs

- Darken keeps the alpha of the color
- GetAllValuesAndDescriptions(Type) uses the [Description] attribute like the generic version
- UrlFriendly cuts titles at 80 characters instead of 81
- RemapInternationalCharToAscii knows both cases of r, l, d, thorn, sharp s, h and j with accents
- IsGenericType returns false instead of throwing when the base type is not generic
- IsCastableFrom also finds conversion operators declared on the target type
- GetDisplayName keeps the brackets of array types when humanizing
- Updated the utility tests to match

src/Artemis.Core/Extensions/SKColorExtensions.cs

@@ -67,7 +67,7 @@ public static class SKColorExtensions
     {
         c.ToHsl(out float h, out float s, out float l);
         l *= 1f - amount;
-        return SKColor.FromHsl(h, s, l);
+        return SKColor.FromHsl(h, s, l, c.Alpha);
     }
 
     private static byte ClampToByte(float value)

src/Artemis.Core/Extensions/TypeExtensions.cs

@@ -55,7 +55,7 @@ public static class TypeExtensions
         if (type == null)
             return false;
 
-        return type.BaseType?.GetGenericTypeDefinition() == genericType;
+        return type.BaseType is {IsGenericType: true} baseType && baseType.GetGenericTypeDefinition() == genericType;
     }
 
     /// <summary>
@@ -111,9 +111,7 @@ public static class TypeExtensions
             return true;
         if (PrimitiveTypeConversions.ContainsKey(to) && PrimitiveTypeConversions[to].Contains(from))
             return true;
-        bool castable = from.GetMethods(BindingFlags.Public | BindingFlags.Static)
-            .Any(m => m.ReturnType == to && (m.Name == "op_Implicit" || m.Name == "op_Explicit"));
-        return castable;
+        return HasConversionOperator(to, from);
     }
 
     /// <summary>
@@ -141,6 +139,15 @@ public static class TypeExtensions
         return 0;
     }
 
+    private static bool HasConversionOperator(Type to, Type from)
+    {
+        // A conversion operator can be declared on either of the two types
+        return from.GetMethods(BindingFlags.Public | BindingFlags.Static)
+                   .Any(m => m.ReturnType == to && (m.Name == "op_Implicit" || m.Name == "op_Explicit")) ||
+               to.GetMethods(BindingFlags.Public | BindingFlags.Static)
+                   .Any(m => m.ReturnType == to && (m.Name == "op_Implicit" || m.Name == "op_Explicit") && m.GetParameters()[0].ParameterType.IsAssignableFrom(from));
+    }
+
     /// <summary>
     ///     Returns the default value of the given type
     /// </summary>
@@ -200,6 +207,10 @@ public static class TypeExtensions
     /// <returns></returns>
     public static string GetDisplayName(this Type type, bool humanize = false)
     {
+        // Name the element type separately so humanizing doesn't drop the brackets
+        if (type.IsArray)
+            return $"{type.GetElementType()!.GetDisplayName(humanize)}[{new string(',', type.GetArrayRank() - 1)}]";
+
         if (!type.IsGenericType)
         {
             string displayValue = TypeKeywords.TryGetValue(type, out string? keyword) ? keyword! : type.Name;