The character that has been typed that triggered the formatting on type request. That is not necessarily the last character that got inserted into the document since the client could auto insert characters as well (e.g. like automatic brace completion).
The formatting options.
The position around which the on type formatting should happen.
This is not necessarily the exact position where the character denoted
by the property ch got typed.
The document to format.
The parameters of a DocumentOnTypeFormattingRequest.