[HID] file-pad: implement GetKeystroke -- menus do not read GetState

The pad looked correct and did nothing. Its own log showed A arriving, the
emulator sat on "PRESS (A) BUTTON", and the title never advanced.

Cause: 360 front-ends poll XamInputGetKeystrokeEx, not XamInputGetState. This
title imports both, and its menus use the keystroke path; the driver returned
X_ERROR_EMPTY there, so every scripted press went into the void while GetState
faithfully reported a button nobody asked about.

Implement it edge-triggered, one event per call: KEYUPs for everything released
first, then KEYDOWNs, matching the SDL driver's ordering (so a thumb transition
clears before it sets). Deliberately NO auto-repeat -- scripted input wants
exactly one event per press, and repeat is precisely what makes menu steps
overshoot. Bits without a virtual key (guide, unused) are swallowed rather than
re-offered forever.

Verified on the real game: title -> main menu -> EXTRAS driven entirely from the
pad file, with `[file-pad] keystroke vk=5800 down/up` in the log for each press.

src/xenia/hid/file/file_input_driver.h

@@ -49,6 +49,7 @@
 #include "xenia/base/cvar.h"
 #include "xenia/base/logging.h"
 #include "xenia/hid/input_driver.h"
+#include "xenia/ui/virtual_key.h"
 
 DECLARE_string(pad_file);
 
@@ -129,8 +130,79 @@ class FileInputDriver final : public InputDriver {
     return user_index == 0 ? X_ERROR_SUCCESS : X_ERROR_DEVICE_NOT_CONNECTED;
   }
 
+  // Menus do NOT read the pad through GetState. "PRESS (A) BUTTON" and most
+  // 360 front-ends poll XamInputGetKeystrokeEx, so a driver that only answers
+  // GetState looks completely dead on a title screen while its own log happily
+  // shows the button arriving. Returning X_ERROR_EMPTY here is what made the
+  // first scripted run press A into the void.
+  //
+  // One event per call, edge triggered: KEYUPs for everything released, then
+  // KEYDOWNs for everything pressed, exactly as the SDL driver orders them.
+  // Deliberately NO auto-repeat — scripted input wants precisely one event per
+  // press, and repeat is what makes menu steps overshoot.
   X_RESULT GetKeystroke(uint32_t user_index, uint32_t flags,
                         X_INPUT_KEYSTROKE* out_keystroke) override {
+    const bool user_any = user_index == 0xFF || user_index == 0xFFFFFFFFu;
+    if (!user_any && user_index != 0) {
+      return X_ERROR_DEVICE_NOT_CONNECTED;
+    }
+    if (!out_keystroke) {
+      return X_ERROR_BAD_ARGUMENTS;
+    }
+    Refresh();
+
+    // Bit index in X_INPUT_GAMEPAD::buttons -> virtual key. Order matters: it is
+    // the order multiple simultaneous changes are reported in.
+    static constexpr uint16_t kVk[16] = {
+        uint16_t(ui::VirtualKey::kXInputPadDpadUp),
+        uint16_t(ui::VirtualKey::kXInputPadDpadDown),
+        uint16_t(ui::VirtualKey::kXInputPadDpadLeft),
+        uint16_t(ui::VirtualKey::kXInputPadDpadRight),
+        uint16_t(ui::VirtualKey::kXInputPadStart),
+        uint16_t(ui::VirtualKey::kXInputPadBack),
+        uint16_t(ui::VirtualKey::kXInputPadLThumbPress),
+        uint16_t(ui::VirtualKey::kXInputPadRThumbPress),
+        uint16_t(ui::VirtualKey::kXInputPadLShoulder),
+        uint16_t(ui::VirtualKey::kXInputPadRShoulder),
+        0, /* guide  */
+        0, /* unused */
+        uint16_t(ui::VirtualKey::kXInputPadA),
+        uint16_t(ui::VirtualKey::kXInputPadB),
+        uint16_t(ui::VirtualKey::kXInputPadX),
+        uint16_t(ui::VirtualKey::kXInputPadY),
+    };
+
+    const uint16_t changed = static_cast<uint16_t>(buttons_ ^ reported_);
+    if (!changed) {
+      return X_ERROR_EMPTY;
+    }
+    for (int pass = 0; pass < 2; ++pass) {
+      const bool clear_pass = pass == 0;
+      for (uint8_t i = 0; i < 16; ++i) {
+        const uint16_t bit = static_cast<uint16_t>(1u << i);
+        if (!(changed & bit) || kVk[i] == 0) {
+          continue;
+        }
+        const bool pressed = (buttons_ & bit) != 0;
+        if (clear_pass == pressed) {
+          continue;
+        }
+        reported_ = static_cast<uint16_t>(pressed ? (reported_ | bit)
+                                                  : (reported_ & ~bit));
+        out_keystroke->virtual_key = kVk[i];
+        out_keystroke->unicode = 0;
+        out_keystroke->flags =
+            pressed ? X_INPUT_KEYSTROKE_KEYDOWN : X_INPUT_KEYSTROKE_KEYUP;
+        out_keystroke->user_index = 0;
+        out_keystroke->hid_code = 0;
+        XELOGI("[file-pad] keystroke vk={:04X} {}", kVk[i],
+               pressed ? "down" : "up");
+        return X_ERROR_SUCCESS;
+      }
+    }
+    // Only bits without a virtual key changed (guide/unused): swallow them so
+    // the caller is not asked again forever.
+    reported_ = buttons_;
     return X_ERROR_EMPTY;
   }
 
@@ -249,6 +321,8 @@ class FileInputDriver final : public InputDriver {
   uint8_t lt_ = 0, rt_ = 0;
   int16_t lx_ = 0, ly_ = 0, rx_ = 0, ry_ = 0;
   uint32_t packet_ = 1;
+  // Buttons already reported through GetKeystroke; the edge detector's memory.
+  uint16_t reported_ = 0;
   bool present_ = false;
   time_t mtime_sec_ = 0;
   long mtime_nsec_ = -1;