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/resources/api/luau/preset_runtime.luau

@@ -0,0 +1,18 @@
+--!strict
+
+--- Contains types and function stubs for building presets. The actual function implementations are provided 
+--- by the runtime.
+local module = {}
+
+--- Returns the content of the given file as string.
+---
+--- The given path is always relative to the module root.
+---
+--- This function is very useful when you build a preset in which the compartment contains commona Lua code.
+--- Instead of writing the common Lua code as a Lua string, you can include it from a dedicated file. That way,
+--- you can benefit from syntax highlighting and typechecking when building the common Lua code.
+function module.include_str(path: string): string?
+    return nil
+end
+
+return module