What does this PR do?

Fixes key ordering quick fix cases where applying the fix breaks YAML layout or fail to apply.

1. Reordering now keeps entries properly separated, one key per line.
   Note that the one key per line is a newly added behavior. To make behavior consistent (I think), I made the rewriter to strip leading blank-line from entries so reordered entries stay one-per-line.
   For example, given:

   one:
     child: moo
   two:
     child: moo
   
   three:
     child: moo

   After reordering keys, we now get:

   one:
     child: moo
   three:
     child: moo
   two:
     child: moo

2. Reordering now works correctly when the map ends at EOF with a trailing newline. Previously, the quick fix could appear but produce no change when click-onto for inputs like (note the blank line at EOF):

   one:
     child: moo
   two:
     child: moo
   three:
     child: moo
       

   Fixes by normalizing newline token handling at map boundaries and applying the replacement over the correct map range so the edit is always effective.

What issues does this PR fix or reference?

Fixes #1171

Is it tested? How?

Automated test + I tested manually.