Add guidebook protodata tag: embed prototype values in guidebook text (#27570)

* First clumsy implementation of guidebook protodata

* Support for Properties, format strings

* Better null

* Rename file

* Documentation and some cleanup

* Handle errors better

* Added note about client-side components

* A couple of examples

* DataFields

* Use attributes like a sane person

* Outdated doc

* string.Empty

* No IComponent?

* No casting

* Use EntityManager.ComponentFactory

* Use FrozenDictionary

* Cache tagged component fields

* Iterate components and check if they're tagged

Content.Shared/Guidebook/GuidebookDataAttribute.cs

@@ -0,0 +1,12 @@
+namespace Content.Shared.Guidebook;
+
+/// <summary>
+/// Indicates that GuidebookDataSystem should include this field/property when
+/// scanning entity prototypes for values to extract.
+/// </summary>
+/// <remarks>
+/// Note that this will not work for client-only components, because the data extraction
+/// is done on the server (it uses reflection, which is blocked by the sandbox on clients).
+/// </remarks>
+[AttributeUsage(AttributeTargets.Field | AttributeTargets.Property)]
+public sealed class GuidebookDataAttribute : Attribute { }