Intent of pieceTreeTextBuffer.test|title=prefix sum for line feed delete random bug 1: I forgot to update the lineFeedCnt when deletion is on one single piece.|occurrence=1

All 1 exact test in this concept. Every test is marked by where it enters the hierarchy.

mocha:v1|namespace=vscode@05c208e9e28d8c1c723fa08f85e2b7a96092e8e5|file=vs/ 1 test
- editor/ 1 test
  - test/ 1 test
    
    common/ 1 test
    
    model/ 1 test
    
    pieceTreeTextBuffer/ 1 test
    
    mocha:v1|namespace=vscode@05c208e9e28d8c1c723fa08f85e2b7a96092e8e5|file=vs/editor/test/common/model/pieceTreeTextBuffer/pieceTreeTextBuffer.test|title=prefix sum for line feed delete random bug 1: I forgot to update the lineFeedCnt when deletion is on one single piece.|occurrence=1 Introduced here