Implement canonical formatter (#1107)

CLI commands also added: `pkl format check` and `pkl format apply`.

pkl-formatter/src/test/files/FormatterSnippetTests/output/spaces.pkl

@@ -0,0 +1,23 @@
+import "foo.pkl"
+
+bar = new Listing<Int>(!isEmpty) { 1; 2 } //a bar
+
+typealias Typealias = (String, Int) -> Boolean
+
+/// a baz
+/// returns its parameter
+baz = (x, y, z) -> x + y + z
+
+function fun(x: Int?, b: Boolean) = if (b) /***return x**/ x else x + bar[0]
+
+prop = trace(1) + super.foo + module.foo
+
+prop2 {
+  for (x in List(1)) {
+    when (x == 1) {
+      x
+    }
+  }
+}
+
+choices: "foo" | *"bar" | String