vim-patch:partial:9.0.0013: reproducing memory access errors can be difficult

Problem:    Reproducing memory access errors can be difficult.
Solution:   When testing, copy each line to allocated memory, so that valgrind
            can detect accessing memory before and/or after it.  Fix uncovered
            problems.

fa4873ccfc

Since test_override() is N/A, enable ml_get_alloc_lines when ASAN is
enabled instead, so it also applies to functional tests.

Use xstrdup() to copy the line as ml_line_len looks hard to port.

Squash the test changes from patch 9.0.0016.

Co-authored-by: Bram Moolenaar <Bram@vim.org>

src/nvim/edit.c

@@ -4653,9 +4653,9 @@ int ins_copychar(linenr_T lnum)
   }
 
   // try to advance to the cursor column
+  validate_virtcol();
   line = ml_get(lnum);
   prev_ptr = line;
-  validate_virtcol();
 
   chartabsize_T cts;
   init_chartabsize_arg(&cts, curwin, lnum, 0, line, line);