feat(markdon): Document missing named exports in core

markdown/dev/reference/api/utils/gettransformedbounds/en.md

@@ -0,0 +1,22 @@
+---
+title: getTransformedBounds
+---
+
+This methods re-calculates the bounding box of an object (a stack or a part) after applying the passed-in transform(s).
+
+The object passed in should have its `topLeft` and `bottomRight` properties set.
+It will return on object that with (only) the updated `topLeft` and `bottomRight` properties set.
+
+## Signature
+
+```js
+Object getTransformedBounds(
+  Object stack,
+  Array transforms
+)
+```
+
+<Note compact>
+This is a low-level method to facilitate intervening in the pattern layout late in the draft process.
+It is unlikely you will want to use this.
+</Note>