tvOS: build ocean's imageio and platform/apple for appletvos

Summary:
Prerequisite for the InstagramTV tvOS app. `xplat/ocean/impl/ocean/media/imageio`
and `xplat/ocean/impl/ocean/platform/apple` both declared
`compatible_with = [iphoneos, macos]`, which hard-fails buck2 analysis the moment
anything reaches them from an appletvos configuration. They are ImageIO,
CoreGraphics and Foundation wrappers, and all three frameworks exist on tvOS, so
appletvos is added to `compatible_with` and APPLETVOS to `apple_sdks`.

`ocean/base/Base.h` additionally classified tvOS as iOS, because Apple sets
TARGET_OS_IPHONE (and TARGET_IPHONE_SIMULATOR on the tvOS simulator) to 1 there.
That made ocean compile UIKit paths tvOS does not provide. A TARGET_OS_TV branch
is added ahead of the iOS ones, with the matching platform string in `Build.cpp`.

This is split out of D114947077 and placed at the bottom of the stack on purpose.
InstagramTV's story tray (D113821281) is what first pulls ocean's imageio into the
tvOS app closure, via IGStoryTraySection -> ... -> CTSmartCreationUtils. With the
fix sitting above that diff, the InstagramTV CI target failed on D113821281, and
more importantly it would have broken the tvOS build on master for the window
between D113821281 landing and D114947077 landing, since diffs land bottom-to-top.

Owned by the `ocean` oncall — flagging for their review. No behaviour change on
iOS, macOS or Android: the only new configuration is appletvos, which previously
could not build these targets at all.

Differential Revision: D115018853

fbshipit-source-id: d5ca2bdf448d3b0d144c5b5687322c23e90e1132

Author: clocksarestupid

impl/ocean/base/Base.h

@@ -604,7 +604,14 @@ inline constexpr bool oceanFalse()
 
 	#define OCEAN_PLATFORM_BUILD_APPLE
 
-	#if defined(TARGET_IPHONE_SIMULATOR) && TARGET_IPHONE_SIMULATOR == 1
+	// tvOS must be tested before the iOS branches: Apple sets TARGET_OS_IPHONE (and
+	// TARGET_IPHONE_SIMULATOR on the tvOS simulator) to 1 there, so without this tvOS would
+	// be classified as iOS and would pull in UIKit APIs that tvOS does not provide.
+	#if defined(TARGET_OS_TV) && TARGET_OS_TV == 1
+
+		#define OCEAN_PLATFORM_BUILD_APPLE_TVOS
+
+	#elif defined(TARGET_IPHONE_SIMULATOR) && TARGET_IPHONE_SIMULATOR == 1
 
 		#define OCEAN_PLATFORM_BUILD_APPLE_IOS_SIMULATOR
 

impl/ocean/base/Build.cpp

@@ -31,6 +31,10 @@ std::string Build::platformType()
 
 	return std::string("ios");
 
+#elif defined(OCEAN_PLATFORM_BUILD_APPLE_TVOS)
+
+	return std::string("tvos");
+
 #elif defined(OCEAN_PLATFORM_BUILD_APPLE_MACOS)
 
 	return std::string("osx");