doAssert, assert now print full path of failing line on error (#8555)

tests/assert/testhelper.nim

@@ -0,0 +1,12 @@
+from strutils import endsWith, split
+from ospaths import isAbsolute
+
+proc checkMsg*(msg, expectedEnd, name: string)=
+  let filePrefix = msg.split(' ', maxSplit = 1)[0]
+  if not filePrefix.isAbsolute:
+    echo name, ":not absolute: `", msg & "`"
+  elif not msg.endsWith expectedEnd:
+    echo name, ":expected suffix:\n`" & expectedEnd & "`\ngot:\n`" & msg & "`"
+  else:
+    echo name, ":ok"
+