Change Signature - Add parameter

[ivanbasov]

Updates the existing Change Signature dialog to allow for the adding of a required parameter (in addition to the existing reorder/remove capabilities). Optional parameters will come as a later update.

The updated Change Signature dialog includes the new "Add" button, as well as two new columns in the datagrid. The "Index" column shows which parameters are new, as well as the original index of preexisting parameters. The "Call site" column shows what value will be put into call sites for this new parameter.

And here is the new Add Parameter dialog itself:

The first two fields both have completion enabled.

TODO for this PR:

• Manual test pass [D & M]
• UI
  • VB support [A]
    • Preview
    • Name field shouldn't have completion (in VB only)
  • Design of completion list text boxes [I+J]
  • UX Review
  • Accessibility [D]
    • Add Parameter dialog
    • Change Signature dialog updates
• Engine
  • Update engine for required parameters (C# & VB) [I]
  • Hook up the simple "TODO" case
• Most Tests
  • Fix broken unit tests [I]
  • Add new engine unit tests [I]
    • C# unit tests
      • Similar to reorder tests
      • Similar to reorder cascading tests
      • Formatting tests
      • Delegates tests
    • VB unit tests

Pre-Dogfood:

• UI
  • Backspacing too much crashes [D] -- PR to Editor pending
• Further testing
  • Unit testing of elision buffer creation
  • Update integration tests [A]
  • Add UI unit tests (when supporting optional parameters) [D]
• Optional Parameters (Larger UI + Engine updates)
• Engine
  • Type binding in all contexts, Expand/Reduce namespace/imports (?)

16.6P1:

• UI
  • Consider the C# UI bug when filling out name before type [A]
  • Meet UX expectations
• Change VS menu from Remove/Reorder Parameters to Change Signature [work with editor]
• Engine
  • Handle multiple TODOs

[dpoeschl]

This review is tooooooo big. If you want to offer further comments, please see these new separated reviews:

Product Code: #42291
Test Code: #42290