Consistently added "-error" suffix in regression test error case filenames

The `.cpp2` cases that should generate errors and not output a valid `.cpp` file all now end with `-error.cpp2`

Author: hsutter

regression-tests/mixed-initialization-safety-1.cpp2 renamed to regression-tests/mixed-initialization-safety-1-error.cpp2

@@ -1,3 +1,6 @@
+REM This is intended to be run in the /test-results directory
+REM A copy is in the parent directory just for convenience in case of accidental deletion.
+REM
 @echo off
 copy ..\*.cpp2 .
 set count=0

regression-tests/mixed-initialization-safety-2.cpp2 renamed to regression-tests/mixed-initialization-safety-2-error.cpp2

@@ -0,0 +1,4 @@
+mixed-initialization-safety-1-error.cpp2...
+mixed-initialization-safety-1-error.cpp2(30,21): error: local variable x is used before it was initialized
+  ==> program violates initialization safety guarantee - see previous errors
+