Feature: Native 1:1 PS4 Touchpad Mapping for DS Touchscreen

[Appltron]

The Concept
Playing touch-heavy games on a monitor can feel clunky when using a mouse to mimic quick stylus taps. This PR introduces native, absolute 1:1 coordinate mapping using a DualShock 4 controller's built-in touchpad via Bluetooth.

This implementation takes heavy inspiration from 3DS emulation fork Azahar, which has proven how seamless and natural absolute touchpad integration feels for dual-screen emulation.

Implementation Details
Instead of building a complex event loop, this leverages SDL2's internal state tracker directly within the EmuThread.cpp loop, right before emuInstance->isTouching is evaluated:

Uses SDL_GameControllerGetTouchpadFinger() to instantly query the absolute position of the primary finger.

Converts SDL's normalized decimal coordinates (0.0 to 1.0) into the rigid 256x192 pixel space of the DS bottom screen using standard aspect compression.

Automatically clamps boundaries to prevent out-of-bounds emulator crashes.

Seamlessly hands control back to the mouse upon finger lift (padWasTouching flag) so users can switch between mouse and touchpad dynamically.

Testing Environment

OS: Windows 11

Hardware: HP ProBook 445 G8 (Ryzen 5 5600U, 16GB RAM)

Controller: Original DualShock 4 via Bluetooth

Build Toolchain: MSYS2 / MinGW-w64 (Compiled via CMake + Ninja)

A Note on Development
Transparency note: I am not a career C++ software engineer, so I utilized an AI assistant to help draft the precise SDL2 API calls and coordinate math. However, I have fully compiled the source code from scratch, resolved the MSYS2 toolchain dependencies, and extensively tested the compiled .exe on hardware to verify the touch inputs register flawlessly without performance dips.

[asiekierka]

This is redundant. The default is the value of [SDL_HINT_JOYSTICK_HIDAPI](https://wiki.libsdl.org/SDL2/SDL_HINT_JOYSTICK_HIDAPI) => "1": HIDAPI drivers are used (the default).

[Appltron]

Thank you for pointing this out. I was unaware it was the default behavior. I have removed the redundant line in the latest commit.