Malformed-XML error messages no longer have filename + location

[rainersigwald]

The error message for bad XML is missing the filename, line, and column location that it used to have.

I suspect this is due to the changes in #1004 (the XmlTextReader we're using no longer knows the path of the file, because we're giving it a stream instead.

Expected and actual output

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003"
      DefaultTargets="t1">
  <Target Name="t1">
    <Message Text= [p2.t1]/>
  </Target>
  <Target Name="t2">
    <Message Text="[p2.t2]"/>
  </Target>
</Project>

Current:

S:\work\1244940>\msbuild\bin\Bootstrap\15.0\Bin\MSBuild.exe pE.proj
Microsoft (R) Build Engine version 15.1.0.0
Copyright (C) Microsoft Corporation. All rights reserved.

Build started 10/31/2016 11:14:10 AM.
Project "S:\work\1244940\pE.proj" on node 1 (default targets).
MSBUILD : error MSB4025: The project file could not be loaded. '[' is an unexpected token. The expected token is '"' or '''. Line 4, position 26. [S:\work\1244940\pE.proj]
Done Building Project "S:\work\1244940\pE.proj" (default targets) -- FAILED.


Build FAILED.

"S:\work\1244940\pE.proj" (default target) (1) ->
  MSBUILD : error MSB4025: The project file could not be loaded. '[' is an unexpected token. The expected token is '"' or '''. Line 4, position 26. [S:\work\1244940\pE.proj]

    0 Warning(s)
    1 Error(s)

Time Elapsed 00:00:00.23

MSBuild 14:

S:\work\1244940>MSBuild.exe pE.proj
Microsoft (R) Build Engine version 14.0.25420.1
Copyright (C) Microsoft Corporation. All rights reserved.

Build started 10/31/2016 11:14:39 AM.
Project "S:\work\1244940\pE.proj" on node 1 (default targets).
S:\work\1244940\pE.proj(4,26): error MSB4025: The project file could not be loaded. '[' is an unexpected token. The expected token is '"' or '''. Line 4, position 26.
Done Building Project "S:\work\1244940\pE.proj" (default targets) -- FAILED.


Build FAILED.

"S:\work\1244940\pE.proj" (default target) (1) ->
  S:\work\1244940\pE.proj(4,26): error MSB4025: The project file could not be loaded. '[' is an unexpected token. The expected token is '"' or '''. Line 4, position 26.

    0 Warning(s)
    1 Error(s)

Time Elapsed 00:00:00.02