Native iPhone port of Factorio 2.0.77

Run the original macOS ARM64 game code on iOS:
- tools/retarget.py: header-only Mach-O retargeting to an iOS dylib
- platform/native: UIKit host and macOS API shims (AppKit for SDL's
  Cocoa backend, CoreGraphics displays, CoreAudio device, Metal device
  properties, Wuffs PNG decoding, Steam and peripheral stubs)
- touch, overlay, iOS keyboard and hardware keyboard input
- tools/build_native.py: build, sign, install, data copy, launch
- docs: build guide, controls, architecture

Also includes the earlier static-translation research (ARM64 -> WASM ->
native) under docs/research, runtime/, tests/ and tools/.

No game files are included; the build reads them from a local install.

platform/native/shim/stack.s

@@ -0,0 +1,18 @@
+// void fx_call_on_stack(void *stack_top, void (*fn)(void *), void *arg)
+// Calls fn(arg) with sp moved to stack_top on the current thread, then restores sp.
+.text
+.globl _fx_call_on_stack
+.p2align 2
+_fx_call_on_stack:
+    stp x29, x30, [sp, #-16]!
+    mov x29, sp
+    mov x9, sp
+    and x0, x0, #~15
+    mov sp, x0
+    stp x9, xzr, [sp, #-16]!
+    mov x0, x2
+    blr x1
+    ldp x9, xzr, [sp], #16
+    mov sp, x9
+    ldp x29, x30, [sp], #16
+    ret