Readfile: Make 'alloc name' for ID type automatically generated.

Avoids having yet another `switch` case over all ID types.

Note that we could also add a string to the IDTypeInfo, but imho this is
a bit too limited in scope/interest to expose this outside of the readfile
code.

@@ -2487,2 +2406,2 @@
-  }
-  return "Data from Lib Block";
+  static const std::array<std::string, INDEX_ID_MAX> id_alloc_names = [] {
+    auto n = decltype(id_alloc_names){};

@@ -2489,0 +2411,4 @@
+        n[size_t(idtype_index)] = std::string("Data from '") + idtype_info->name + "'";
+      }
+      else {
+        n[size_t(idtype_index)] = "Data from UNKNWOWN ID Type";

@@ -2487,0 +2420,4 @@
+    return n;
+  }();
+
+  const size_t idtype_index(size_t(BKE_idtype_idcode_to_index(id_code)));