Support Basic Inlay Hints

[Rosemoe]

Modern IDEs use inlay hints to help user keep track of params, variable types and scopes, etc.
For example, in IDEA, you will notice inlay hints like these:

• Inlay hints in line:
  
• Inlay hints above line:
  

Also, you can interact with inlay hints by click or long-press them.
And basically, all inlay hints should be measurable. But as editor is a View but not ViewGroup, we will get limited functionality of these inlay hints.