feat(pad): touch the left or right touchpad half from the input command file

APS5_PAD_INPUT_FILE commands can set bit 0x200000 or 0x400000 to put a
finger on the left or right half of the touchpad, as the TouchLeft and
TouchRight keys do, so scripted runs can press touchpad combinations.
tools/pad_input.py queues them as touch-left and touch-right.

AI-assisted: yes

docs/user/USAGE.md

@@ -144,9 +144,10 @@ python3 tools/pad_input.py /tmp/anyps5-pad down --hold-ms 500
 python3 tools/pad_input.py /tmp/anyps5-pad release
 python3 tools/pad_input.py /tmp/anyps5-pad release --left-stick 128 0 --hold-ms 2000
 python3 tools/pad_input.py /tmp/anyps5-pad cross --left-stick 255 128 --right-stick 0 128
+python3 tools/pad_input.py /tmp/anyps5-pad touch-right
 ```
 
-Run the helper in a second terminal. Commands are polled at most every 100 ms during controller reads, and their buttons add to physical controller input. A press lasts 300 ms by default, starting when the application reads it, and releases automatically; `--hold-ms` accepts 1–5000 ms. `--left-stick X Y` and `--right-stick X Y` hold the sticks for the same time: each axis is 0-255, 128 is the centre, X grows to the right and Y grows downward. While such a command is active both sticks come from it instead of the physical controller, and a stick that was not named stays centred. Wait for the application to observe a release before sending another press. The file holds only the latest command; rapid commands can replace one another. On POSIX, replacing an existing command file retains its permission mode; a privileged helper also retains its owner and group so the game user can still read it. Commands left over when the application first reads the controller are ignored. Without the environment variable, file input is disabled.
+Run the helper in a second terminal. Commands are polled at most every 100 ms during controller reads, and their buttons add to physical controller input. A press lasts 300 ms by default, starting when the application reads it, and releases automatically; `--hold-ms` accepts 1–5000 ms. `--left-stick X Y` and `--right-stick X Y` hold the sticks for the same time: each axis is 0-255, 128 is the centre, X grows to the right and Y grows downward. While such a command is active both sticks come from it instead of the physical controller, and a stick that was not named stays centred. `touch-left` and `touch-right` press the touchpad with a finger on its left or right half, as the `TouchLeft` and `TouchRight` keys do; in the command file they are bits `0x200000` and `0x400000` of the button field. Wait for the application to observe a release before sending another press. The file holds only the latest command; rapid commands can replace one another. On POSIX, replacing an existing command file retains its permission mode; a privileged helper also retains its owner and group so the game user can still read it. Commands left over when the application first reads the controller are ignored. Without the environment variable, file input is disabled.
 
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