Models builder: Move InMemoryAuto models builder and razor runtime compilation into its own package to enable hot reload (#20187)

* Move in memory models builder out of core

* Move runtime validations into backoffice development project

* Obsolete ModelsMode enum

* Move the InMemoryModelsbuilder/RRC novel into the Backoffice development umbraco builder extension

* Add runtime validator to warn if InMemoryAuto is selected but the package isn't installed

* Add backoffice development to template

* Remove propertyGroup

* Remove oopsie

* Check for modelsbuilder in notification handler instead of runtime validator

* Update src/Umbraco.Cms.Api.Management/Controllers/ModelsBuilder/BuildModelsBuilderController.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update src/Umbraco.Infrastructure/Runtime/RuntimeModeValidators/ModelsBuilderModeValidator.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Remove ModelsMode enum and ModelsModeExtensions

* Apply suggestions from code review

Co-authored-by: Kenn Jacobsen <kja@umbraco.dk>

* Move project to source folder

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Kenn Jacobsen <kja@umbraco.dk>

src/Umbraco.Cms.DevelopmentMode.Backoffice/InMemoryAuto/ModelsBuilderAssemblyAttribute.cs

@@ -0,0 +1,20 @@
+namespace Umbraco.Cms.DevelopmentMode.Backoffice.InMemoryAuto;
+
+/// <summary>
+///     Indicates that an Assembly is a Models Builder assembly.
+/// </summary>
+[AttributeUsage(AttributeTargets.Assembly /*, AllowMultiple = false, Inherited = false*/)]
+public sealed class ModelsBuilderAssemblyAttribute : Attribute
+{
+    /// <summary>
+    ///     Gets or sets a value indicating whether the assembly is a InMemory assembly.
+    /// </summary>
+    /// <remarks>A Models Builder assembly can be either InMemory or a normal Dll.</remarks>
+    public bool IsInMemory { get; set; }
+
+    /// <summary>
+    ///     Gets or sets a hash value representing the state of the custom source code files
+    ///     and the Umbraco content types that were used to generate and compile the assembly.
+    /// </summary>
+    public string? SourceHash { get; set; }
+}