Improve Star Wars Trilogy lightgun and multi-mouse input

[Zer0one]

Summary

Follow-up to #2. This PR improves the dedicated Star Wars Trilogy Arcade
control profile without changing the profiles used by ordinary gun games.

• exposes the same input-source choices available to gun profiles: Standard,
  Lightgun Only, Mouse + Analog Stick, Mouse Only, and Analog Stick Only;
• translates RetroLightgun absolute coordinates, RetroMouse relative motion,
  and the RetroPad left stick into the game's absolute self-centering yoke;
• keeps source ownership deterministic in Standard mode instead of mixing
  simultaneous values;
• maps the cabinet's duplicated Trigger/Event pair to the second Mouse or
  Lightgun port, leaving each device's extra buttons available for common
  Start/Coin inputs;
• applies the optional Upright cabinet X-axis correction after every input
  source converges on the virtual yoke;
• updates the control-profile documentation and runtime input descriptors.

Validation

The exact current head (dbd7b7d) passed the complete four-platform
Libretro Core CI matrix:

• Linux x86_64;
• Windows x86_64;
• macOS x86_64;
• macOS ARM64.

Real-ROM testing covered Star Wars Trilogy Arcade on RetroArch/macOS ARM64 and
Batocera 43.1 x86_64. The five source modes, mouse and analog yoke motion,
Lightgun behavior, Upright X-axis correction, separate Mouse 1/Mouse 2
Trigger/Event inputs, and Coin Chute 1/2 through two physical mice were
verified. The Batocera test used only frontend-side device routing; the core
continues to consume the standard Libretro Mouse and Lightgun APIs.

AI-assisted development disclosure

As with the post-sgiannop integration documented in #2, this follow-up was
developed as an AI-assisted study using OpenAI GPT-5.6 Sol through Codex. The
human maintainer defined the behavior, supplied hardware and real-ROM testing,
evaluated the results, and approved the implementation. The AI system performed
source analysis, implementation, debugging, documentation, and automated
validation. Independent human review is still required; passing CI and runtime
tests should not be treated as proof of correctness.