BKE_file: Add util to check if a given blend file is readable.

`BKE_blendfile_is_readable` attempts to open the given file path, and
return `true` on success, `false` on failure.

Part of #109151 (PR !110109).

source/blender/blenkernel/BKE_blendfile.h

@@ -48,6 +48,13 @@ bool BKE_blendfile_library_path_explode(const char *path,
                                         char **r_group,
                                         char **r_name);
 
+/**
+ * Check whether a given path is actually a Blender-readable, valid .blend file.
+ *
+ * \note Currently does attempt to open and read (part of) the given file.
+ */
+bool BKE_blendfile_is_readable(const char *path, struct ReportList *reports);
+
 /**
  * Shared setup function that makes the data from `bfd` into the current blend file,
  * replacing the contents of #G.main.

source/blender/blenkernel/intern/blendfile.cc

@@ -142,6 +142,18 @@ bool BKE_blendfile_library_path_explode(const char *path,
   return true;
 }
 
+bool BKE_blendfile_is_readable(const char *path, ReportList *reports)
+{
+  BlendFileReadReport readfile_reports;
+  readfile_reports.reports = reports;
+  BlendHandle *bh = BLO_blendhandle_from_file(path, &readfile_reports);
+  if (bh != nullptr) {
+    BLO_blendhandle_close(bh);
+    return true;
+  }
+  return false;
+}
+
 /** \} */
 
 /* -------------------------------------------------------------------- */