NetCore: Refactor config/setting to not use dependencies (#7810)

* Avoid usage of IOHelper in GlobalSettings

* Avoid usage of IOHelper in ModelsBuilderConfig.cs

* Avoid usage of IOHelper in ConnectionStrings.cs

* Simplified more config

* Fix for ModelsBuilderConfig

* Moved GetUmbracoMvcAreaNoCache to IOHelperExtensions

src/Umbraco.Core/Configuration/ModelsBuilderConfigExtensions.cs

@@ -0,0 +1,57 @@
+using System.Configuration;
+using System.IO;
+using Umbraco.Core.IO;
+
+namespace Umbraco.Core.Configuration
+{
+    public static class ModelsBuilderConfigExtensions
+    {
+        private static string _modelsDirectoryAbsolute = null;
+
+        public static string ModelsDirectoryAbsolute(this IModelsBuilderConfig modelsBuilderConfig, IIOHelper ioHelper)
+        {
+
+            if (_modelsDirectoryAbsolute is null)
+            {
+                var modelsDirectory = modelsBuilderConfig.ModelsDirectory;
+                var root = ioHelper.MapPath("~/");
+
+                _modelsDirectoryAbsolute = GetModelsDirectory(root, modelsDirectory,
+                    modelsBuilderConfig.AcceptUnsafeModelsDirectory);
+            }
+
+            return _modelsDirectoryAbsolute;
+        }
+
+        // internal for tests
+        internal static string GetModelsDirectory(string root, string config, bool acceptUnsafe)
+        {
+            // making sure it is safe, ie under the website root,
+            // unless AcceptUnsafeModelsDirectory and then everything is OK.
+
+            if (!Path.IsPathRooted(root))
+                throw new ConfigurationErrorsException($"Root is not rooted \"{root}\".");
+
+            if (config.StartsWith("~/"))
+            {
+                var dir = Path.Combine(root, config.TrimStart("~/"));
+
+                // sanitize - GetFullPath will take care of any relative
+                // segments in path, eg '../../foo.tmp' - it may throw a SecurityException
+                // if the combined path reaches illegal parts of the filesystem
+                dir = Path.GetFullPath(dir);
+                root = Path.GetFullPath(root);
+
+                if (!dir.StartsWith(root) && !acceptUnsafe)
+                    throw new ConfigurationErrorsException($"Invalid models directory \"{config}\".");
+
+                return dir;
+            }
+
+            if (acceptUnsafe)
+                return Path.GetFullPath(config);
+
+            throw new ConfigurationErrorsException($"Invalid models directory \"{config}\".");
+        }
+    }
+}