Allow docCommentTemplate before Function Expressions

[mjbvz]

From microsoft/vscode#21237

TypeScript Version: 2.2.1

Code

(
|
 function add(a, b) {}   
)

Request docCommentTemplate from TSServer at the |

Expected behavior:
Returns a template with the parameters for add

Actual behavior:
Since the docCommentTemplate is requested inside of an expression, no result is returned. Reading through the implementation of docCommentTemplate, this seems to be by-design currently