Add ability to install prebuilt ninja

We may start using it internally in emscripten. See
emscripten-core/emscripten#17809

Author: sbc100

emsdk_manifest.json

@@ -626,6 +626,16 @@
     "activated_cfg": "MINGW_ROOT='%installation_dir%'",
     "activated_path": "%installation_dir%/bin"
   },
+  {
+    "id": "ninja",
+    "version": "1.11.1",
+    "bitness": 64,
+    "windows_url": "ninja-1.11.1-win.zip",
+    "linux_url": "ninja-1.11.1-linux.zip",
+    "macos_url": "ninja-1.11.1-mac.zip",
+    "activated_cfg": "NINJA_ROOT='%installation_dir%'",
+    "activated_path": "%installation_dir%"
+  },
   {
     "id": "ninja",
     "version": "git-release",