Refactor: Move asset editing code into own file and refactor

* Move from paint_ops.cc and asset_weak_reference.cc into asset_edit.cc
* Rename AssetWeakReferenceMain to AssetEditBlend
* Change some functions to be based on ID instead of main pointer
* Make most of save as and update code no longer brush specific.

@@ -0,0 +51,4 @@
+    const ID *id,
+    const char *name,
+    std::optional<blender::asset_system::CatalogID> catalog_id,
+    std::optional<const std::string> catalog_simple_name,

@@ -0,0 +37,4 @@
+
+#include "MEM_guardedalloc.h"
+
+using namespace blender;

@@ -0,0 +42,4 @@
+/**
+ * Asset library blend file, with editable contents.
+ */
+

@@ -0,0 +405,4 @@
+  return final_full_asset_filepath;
+}
+
+bool BKE_asset_edit_id_save(Main & /* global_main */, const ID *id, ReportList *reports)

@@ -0,0 +29,4 @@
+#include "AS_asset_catalog.hh"
+
+#include "DNA_ID_enums.h"
+#include "DNA_asset_types.h"

@@ -0,0 +36,4 @@
+struct Main;
+struct ReportList;
+
+/* Get datablock from weak reference, loading the blend file as needed. */

@@ -0,0 +179,4 @@
+  while (BLI_is_file((root_path + SEP + base_name_filesafe + "_" + std::to_string(i++) +
+                      BLENDER_ASSET_FILE_SUFFIX)
+                         .c_str()))
+    ;