Add Swappy & Pre-Transformed Swapchain

- Adds Swappy for Android for stable frame pacing
- Implements pre-transformed Swapchain so that Godot's compositor is in
charge of rotating the screen instead of Android's compositor
(performance optimization for phones that don't have HW rotator)

============================

The work was performed by collaboration of TheForge and Google. I am
merely splitting it up into smaller PRs and cleaning it up.

Changes from original PR:

- Removed "display/window/frame_pacing/android/target_frame_rate" option
to use Engine::get_max_fps instead.
- Target framerate can be changed at runtime using Engine::set_max_fps.
- Swappy is enabled by default.
- Added documentation.
- enable_auto_swap setting is replaced with swappy_mode.

SConstruct

@@ -229,6 +229,7 @@ opts.Add(BoolVariable("use_volk", "Use the volk library to load the Vulkan loade
 opts.Add(BoolVariable("disable_exceptions", "Force disabling exception handling code", True))
 opts.Add("custom_modules", "A list of comma-separated directory paths containing custom modules to build.", "")
 opts.Add(BoolVariable("custom_modules_recursive", "Detect custom modules recursively for each specified path.", True))
+opts.Add(BoolVariable("swappy", "Use Swappy Frame Pacing Library in Android builds.", False))
 
 # Advanced options
 opts.Add(
@@ -611,6 +612,8 @@ if env["dev_mode"]:
 if env["production"]:
     env["use_static_cpp"] = methods.get_cmdline_bool("use_static_cpp", True)
     env["debug_symbols"] = methods.get_cmdline_bool("debug_symbols", False)
+    if platform_arg == "android":
+        env["swappy"] = methods.get_cmdline_bool("swappy", True)
     # LTO "auto" means we handle the preferred option in each platform detect.py.
     env["lto"] = ARGUMENTS.get("lto", "auto")