Add on-screen touch controls

[epic-ship-it]

On-screen touch controls

The app is controller-only today, so a phone without a gamepad can't play it. This
adds a full N64 pad on the touchscreen: analog stick, A/B, the C diamond, L/Z/R,
Start, and a settings handle.

With a gamepad nothing changes, and the new Off mode is the existing behaviour.

How it works

The overlay presents itself as an extra SDL game controller: a button mask and an
axis array, merged inside controller_button_state() and controller_axis_state(),
the two functions every physical pad already goes through. That's 28 added lines in
input.cpp and nothing removed.

So every binding in Settings → Controls applies to the on-screen buttons, a rebind
can't detach them, they combine with a physical pad the way two pads do, and analog
camera, C-button masking and mods don't need changes.

• The C cluster emits D-pad. Of C's three stock bindings it's the only one that
  covers all four directions (C-Right has no face button) and still works in
  analog-camera mode.
• The menu toggle is event-driven while gameplay is polled, so the handle queues a
  real controller event. It opens and closes the menu and follows a rebind of
  Toggle Menu.
• It's an Android View over SDL's SurfaceView, drawn as vectors, so the APK
  doesn't grow and the native build isn't involved in layout changes.

Settings

A new Touch tab, gated on touch_supported like the GPU Driver tab:

• On-Screen Controls — Auto / On / Off. Auto shows the pad until a gamepad is
  used, brings it back on the next touch, and starts hidden if a gamepad is already
  attached.
• Stick Sensitivity — the stick is about 9 mm across on a 450 dpi phone, so a
  linear response fits the whole walking range into about 4.5 mm. The magnitude is
  raised to a gamma (default 50 → 1.75). Full tilt is still reached at the rim.
• Edit Layout — drag controls over the running game; tap one and use −/+ to
  resize it.

It's a separate tab because this menu's option list doesn't scroll by drag, so rows
below the fold on General can't be reached without a gamepad. Long-pressing the
handle opens size, opacity and vibration.

Tested

On an Adreno 650 device running Android 13, with Framebuffer Effects off per the
README's Adreno note:

• buttons and stick drive the game; the default stick sensitivity allows walking
• the handle opens and closes the menu, and the overlay hides while the menu is open
• Off removes the overlay, Edit Layout works with Off selected, and layout changes
  persist
• with no gamepad attached, the overlay starts visible

Not tested:

• with a physical gamepad attached (auto-hide, starting hidden, touch and pad
  together)
• other GPUs or Android versions
• desktop builds (the tab is gated off and the input.cpp merge is Android-only)

[epic-ship-it]

@ogdanimal hey man, love your android fork, i added on-screen touch controls so i could play on my phone