[analysis_server] Remove useLineEndingsForPlatform=false from outline tests

+ remove hard-coded values and replace with TestCode ranges.

Change-Id: I11cad775f35bd97d78adbec02cfa451a45734ded
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/444060
Reviewed-by: Samuel Rawlins <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Samuel Rawlins <[email protected]>

Author: DanTup