[BUG] Fix Dialog title icon alignment

Steps to reproduce

1. Go to https://blueprintjs.com/docs/#core/components/dialog
2. Show Dialog with Title

Actual behavior

Icon in Dialog header is not vertically aligned with content. Here a screenshot:

Now:

Expected behavior

Expected:

Possible solution

For Dialog the negative margin left -4px should disappear so dialog icon title and dialog content is vertically aligned.