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/vim9.h

@@ -499,12 +499,19 @@ typedef struct {
     class_T	*cm_class;
     int		cm_idx;
 } classmember_T;
+
 // arguments to ISN_STOREINDEX
 typedef struct {
     vartype_T	si_vartype;
     class_T	*si_class;
 } storeindex_T;
 
+// arguments to ISN_LOCKUNLOCK
+typedef struct {
+    char_u	*string;	// for exec_command
+    int		is_arg;		// is lval_root a function arg
+} lockunlock_T;
+
 /*
  * Instruction
  */
@@ -561,6 +568,7 @@ struct isn_S {
 	construct_T	    construct;
 	classmember_T	    classmember;
 	storeindex_T	    storeindex;
+	lockunlock_T	    lockunlock;
     } isn_arg;
 };