Implement canonical formatter (#1107)

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

pkl-formatter/src/test/files/FormatterSnippetTests/output/comment-interleaved.pkl

@@ -0,0 +1,34 @@
+module comment.interleaved
+
+local test: Int | String =
+  if (true)
+    1 // It's the same as "100%"
+  else
+    "8%"
+
+foo: ( // some comment
+  *String(
+    // if dtstart is defined and a datetime, until must also be a datetime if defined
+    true,
+  )
+    | Int
+  // trailing comment
+)?
+
+foo2: ( // some comment
+  Int, // other comment
+  String,
+) ->
+  Int
+
+bar =
+  ( // some comment
+    10 + 10
+    // another comment
+  )
+
+bar2 = ( // some comment
+  foo,
+  bar
+  // another comment
+) -> foo + bar