Make InsertText wait for changes

Currently if you are making a lot of changes to the same file you need to either use Start-Sleep after each call or watch FileContext for the changes to show. Otherwise it won't be inserted in the correct position.

This can be demonstrated by running:

# These characters will be inserted in a random order.
'abcdefg'.ToCharArray() | % { $psEditor.GetEditorContext().CurrentFile.InsertText($_) }

从 CurrentFile.InsertText 入口点开始，使用正文中所示的 PowerShell 管道重现该问题。该 issue 未指定源文件或测试；完成的标准是：在不使用 Start-Sleep 或监视 FileContext 的情况下，对一个文件的重复插入按预期顺序完成。