Add a script to install the Vulkan SDK on macOS

This script can be used to make Godot easier to compile on a fresh
macOS installation, including on CI platforms and containers where
the Vulkan SDK isn't preinstalled.

misc/scripts/install_vulkan_sdk_macos.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+IFS=$'\n\t'
+
+# Download and install the Vulkan SDK.
+curl -LO "https://sdk.lunarg.com/sdk/download/latest/mac/vulkan-sdk.dmg"
+hdiutil attach vulkan-sdk.dmg -mountpoint /Volumes/vulkan-sdk
+/Volumes/vulkan-sdk/InstallVulkan.app/Contents/MacOS/InstallVulkan \
+    --accept-licenses --default-answer --confirm-command install
+hdiutil detach /Volumes/vulkan-sdk
+
+echo 'Vulkan SDK installed successfully! You can now build Godot by running "scons".'