patch 9.0.1955: Vim9: lockvar issues with objects/classes

Problem:  Vim9: lockvar issues with objects/classes
Solution: fix `get_lhs()` object/class access and avoid `SEGV`,
          make error messages more accurate.

- `get_lval()` detects/returns object/class access
- `compile_lock_unlock()` generate code for bare static and obj_arg access
- `do_lock_var()` check lval for `ll_object`/`ll_class` and fail if so.

Details:
- Add `ll_object`/`ll_class`/`ll_oi` to `lval_T`.
- Add `lockunlock_T` to `isn_T` for `is_arg` to specify handling of `lval_root` in `get_lval()`.
- In `get_lval()`, fill in `ll_object`/`ll_class`/`ll_oi` as needed; when no `[idx] or .key`, check lval_root on the way out.
- In `do_lock_var()` check for `ll_object`/`ll_class`; also bullet proof ll_dict case
  and give `Dictionay required` if problem. (not needed to avoid lockvar crash anymore)
- In `compile_lock_unlock()` compile for the class variable and func arg cases.

closes: #13174

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Ernie Rael <errael@raelity.com>

src/vim9instr.c

@@ -2169,6 +2169,23 @@ generate_PUT(cctx_T *cctx, int regname, linenr_T lnum)
     return OK;
 }
 
+/*
+ * Generate an EXEC instruction that takes a string argument.
+ * A copy is made of "line".
+ */
+    int
+generate_LOCKUNLOCK(cctx_T *cctx, char_u *line, int is_arg)
+{
+    isn_T	*isn;
+
+    RETURN_OK_IF_SKIP(cctx);
+    if ((isn = generate_instr(cctx, ISN_LOCKUNLOCK)) == NULL)
+	return FAIL;
+    isn->isn_arg.lockunlock.string = vim_strsave(line);
+    isn->isn_arg.lockunlock.is_arg = is_arg;
+    return OK;
+}
+
 /*
  * Generate an EXEC instruction that takes a string argument.
  * A copy is made of "line".