Debug - Unable to hit a breakpoint for git modified files and other oddness

## Environment data
```
dotnet --info
.NET Command Line Tools (1.0.0-preview2-1-003177)

Product Information:
Version: 1.0.0-preview2-1-003177
Commit SHA-1 hash: a2df9c2576

Runtime Environment:
OS Name: Mac OS X
OS Version: 10.10
OS Platform: Darwin
RID: osx.10.10-x64
```
VSCode Version: 2fbc979 Version 1.13.0-insider (1.13.0-insider)
C# Extension version: 1.9.0

## Steps to reproduce
Modify git source controlled file.
Save.
Set breakpoint.
Go to debugger - hit the "play" button to start debugging.
Notice that breakpoint is not hit.
Additionally, when hitting a breakpoint in a non-modified file, then stepping into the git-modified file finds the breakpoint highlight misplaced. This is recent behavior. It used to "work the right way" before.


See Microsoft/vscode/issues/26846