Fix & Enhancements for AddExplicitTypeToParameter

[Booksbaum]

As promised in #917: Fix for AddExplicitTypeToParameter
And some enhancements

Fix: AddExplicitTypeToParameter triggers despite type already specified

Enhancement: Trigger for primary constructor

• secondary ctors (new (...) = ...) already worked

Enhancement: Surround with parens less often

• prev: only don't add parens when already directly surrounded by parens (no spaces allowed) [*1]

  let f1 (a) = a + 1
  //      ^
  let f2 (a ) = a + 1
  //      ^

  =>

  let f1 (a: int) = a + 1
  let f2 ((a: int) )

• now: don't add parens when surrounded by parens or , and spaces somewhere between are ok:

  let f1 (a) = a + 1
  //      ^
  let f2 (a ) = a + 1
  //      ^
  let f3 (a, b, c) = a + b + c + 1
  //         ^
  let f4 (a,  b  ) = a + b + 1
  //          ^

  =>

  let f1 (a: int) = a + 1
  let f2 (a: int ) = a + 1
  let f3 (a, b: int, c) = a + b + c + 1
  let f4 (a,  b: int  ) = a + b + 1

Fix: NamedText.TryGetChar throws exception when Position in last column

---

hmpf...no code in footnotes allowed
-> footnote substitute using custom separator, html and [*1]....

[*1]: Actually there were some more cases it didn't add parens: when other text directly adjacent to identifier and no spaces to next parens:

let f1 (a,b,c) = a + b + c + 1
//        ^

=>

let f1 (a,b:int,c) = a + b + c + 1

But any spaces inside parens and param gets parens:

let f2 (a,b,c ) = a + b + c + 1
//        ^
let f3 (a ,b,c) = a + b + c + 1
//         ^
let f4 (a, b,c) = a + b + c + 1
//         ^

=>

let f2 (a,(b: int),c ) = a + b + c + 1
let f3 (a ,(b: int),c) = a + b + c + 1
let f4 (a, (b: int),c) = a + b + c + 1

With this PR neither of these cases gets parens

[baronfel]

This test suite is awesome. I really appreciate the detail and effort you've put in here to make this codefix consistent and correct!

[baronfel]

When you have such a detailed test suite, it makes it very easy for me to click the merge button. I love your approach here, thank you so much.