Vendor helgoboss/helgobox (ReaLearn) as basis for custom UI fork

Stripped upstream git history; starting point for replacing the native
SWELL/Win32 mapping UI with something more suited to bulk editing.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

plugin-reaper-realearn/doc/svg-gen/modules.dot

@@ -0,0 +1,22 @@
+digraph modules {
+  node [shape = "box"];
+
+  reaper_rs [label = "reaper-rs"]
+  helgoboss_learn [label = "helgoboss-learn"]
+  helgoboss_midi [label = "helgoboss-midi"]
+
+  subgraph cluster_realearn {
+    label = "ReaLearn";
+    main;
+    swell_ui [label = "swell-ui"];
+    api;
+  }
+
+  main -> api;
+  main -> swell_ui;
+  main -> reaper_rs;
+  main -> helgoboss_learn;
+  main -> helgoboss_midi;
+  reaper_rs -> helgoboss_midi;
+  helgoboss_learn -> helgoboss_midi;
+}