Increase C# language version to 12.0 and refactor sources accordingly

Author: YevgeniyShunevych

src/Atata.Configuration.Json/Atata.Configuration.Json.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0</TargetFrameworks>
-    <LangVersion>11.0</LangVersion>
+    <LangVersion>12.0</LangVersion>
     <ImplicitUsings>enable</ImplicitUsings>
     <Version>2.5.0</Version>
     <Description>C#/.NET package for Atata configuration through JSON files.

src/Atata.Configuration.Json/JsonConfig`1.cs

@@ -51,7 +51,7 @@ public DriverJsonSection Driver
         {
             if (value != null)
             {
-                Drivers ??= new List<DriverJsonSection>();
+                Drivers ??= [];
                 Drivers.Add(value);
             }
         }

src/Atata.Configuration.Json/JsonSection.cs

@@ -8,7 +8,7 @@ namespace Atata.Configuration.Json;
 public class JsonSection
 {
     [JsonExtensionData]
-    public Dictionary<string, JToken> AdditionalProperties { get; } = new Dictionary<string, JToken>();
+    public Dictionary<string, JToken> AdditionalProperties { get; } = [];
 
     [JsonIgnore]
     public Dictionary<string, object> ExtraPropertiesMap => AdditionalProperties?.ToDictionary(x => x.Key, x => ConvertJToken(x.Value));

src/Atata.Configuration.Json/Mapping/JsonConfigMapper.cs

@@ -102,7 +102,7 @@ public static AtataContextBuilder Map<TConfig>(TConfig config, AtataContextBuild
         if (config.UseNUnitTestSuiteType)
             builder.UseNUnitTestSuiteType();
 
-        List<string> warnings = new();
+        List<string> warnings = [];
 
         // TODO: v3. Remove all the code below related to NUnit event handlers.
 #pragma warning disable CS0618 // Type or member is obsolete