[debugger] Enable reading embedded ppdb (#32447)

[debugger] Enable reading embedded ppdb (#32447)

To fix the issue of enable reading embedded pdb everywhere the problem was that when the roslyn tests are compiling sources it creates embedded pdb with source file "", and before enable reading the embedded pdb we don't read this information, and now we read and our StackTrace corlib doesn't expect a source file "", it's okay if it's NULL but not "".
I could fix in corlib or in mono, I prefer to fix on mono because I don't know if there is any other place in corlib that doesn't expect source file "".

Co-authored-by: Thays Grazia <thaystg@gmail.com>