nimsuggest: more precise cursor tracking

nimsuggest/tests/tstrutils.nim

@@ -0,0 +1,9 @@
+discard """
+$nimsuggest --tester lib/pure/strutils.nim
+>def lib/pure/strutils.nim:2300:6
+def;;skTemplate;;system.doAssert;;proc (cond: bool, msg: string): typed;;*/lib/system.nim;;*;;9;;"same as `assert` but is always turned on and not affected by the\x0A``--assertions`` command line switch.";;100
+"""
+
+# Line 2300 in strutils.nim is doAssert and this is unlikely to change
+# soon since there are a whole lot of doAsserts there.
+