Adopt extension kind for those extensions defined as ui extensions. For microsoft#85819

Author: aeschli

extensions/vscode-test-resolver/package.json

@@ -8,7 +8,7 @@
 	"engines": {
 		"vscode": "^1.25.0"
 	},
-	"extensionKind": "ui",
+	"extensionKind": [ "ui" ],
 	"scripts": {
 		"compile": "node ./node_modules/vscode/bin/compile -watch -p ./",
 		"vscode:prepublish": "node ../../node_modules/gulp/bin/gulp.js --gulpfile ../../build/gulpfile.extensions.js compile-extension:vscode-test-resolver ./tsconfig.json"