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/main/lib/helgoboss-learn/rustfmt.toml

@@ -0,0 +1,4 @@
+max_width = 100
+#comment_width = 100
+#wrap_comments = true
+#version = "Two"