Fix mistakes in FX API docs

Collection of JavaDoc mistakes. This is the last batch for fixes aimed at 11.

1. Region has a standalone paragraph "A Region with a shape".

2. JDK-8155875

3. JDK-8204950

4. javafx.scene.transform.Rotate is missing the angle argument for its 4th column.

5. The `pickOnBounds` property has `@default false`, but Region overrides it to `true` (this is stated in Region's doc).

6. JDK-8205453

7. ObservableValue: remove unneeded commas before "if" and "that".

8. InvalidationListener: missing period at the end of the first paragraph.

9. WeakInvalidationListener:
 - remove unneeded commas before "if" and "that".
 - "WeakInvalidationListener are created" -> A WeakInvalidationListener is created"
 - "otherwise it will be garbage collected to soon." -> "otherwise it can be garbage collected too soon."

10. ObservableValue: "Important note: attaching a ChangeListener enforces eager computation even if the implementation of the ObservableValue supports lazy evaluation." This is true for InvalidationListener too.

11. Mesh's protected constructor is missing a doc.

12. Color.deriveColor uses the brightness description for the opacity @param