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.

tests/check_a64_guards.py

@@ -0,0 +1,21 @@
+import struct
+import sys
+from pathlib import Path
+sys.path.insert(0, str(Path(__file__).parents[1] / 'tools'))
+from a64_lift import Compiler, UnsupportedInstruction
+
+for words, reason in [([0x14000000, 0xd65f03c0], 'loop with unreachable return'),
+                       ([0x94000000, 0xd65f03c0], 'undeclared host call'),
+                       ([0x91000400], 'missing return'),
+                       ([0xd65f03c0, 0xd503201f], 'code after return'),
+                       ([0x9a010000, 0xd65f03c0], 'unsupported carry arithmetic'),
+                       ([0x9a810000, 0xd65f03c0], 'conditional select without defined flags'),
+                       ([0x3cc18020, 0xd65f03c0], '128-bit load without adjacent store'),
+                       ([0x3d800000, 0xd65f03c0], '128-bit store without adjacent load'),
+                       ([0x14000002, 0x3cc18020, 0x3d800000, 0xd65f03c0], 'branch into middle of copy')]:
+    try:
+        Compiler().compile(b''.join(struct.pack('<I', word) for word in words), 0x1000)
+    except UnsupportedInstruction:
+        print('PASS: rejected', reason)
+    else:
+        raise AssertionError('Unexpected support for ' + reason)