vim-patch:8.1.2281: 'showbreak' cannot be set for one window

Problem:    'showbreak' cannot be set for one window.
Solution:   Make 'showbreak' global-local.
ee85702c10

Change in oneleft() is N/A as the relevant condition was removed
(has_mbyte is always true for Nvim, so the condition was always false;
see commit 73dc9e9).

Use wp over curwin for curs_columns().

Required for v8.2.2903 (otherwise test fails as it'll leave the global
option set).

N/A patches for version.c:

vim-patch:8.1.2283: missed on use of p_sbr

Problem:    Missed on use of p_sbr.
Solution:   Add missing p_sbr change.
91e22eb6e0

Already ported in commit 43a874a.

src/nvim/buffer_defs.h

@@ -230,6 +230,8 @@ typedef struct {
 # define w_p_culopt w_onebuf_opt.wo_culopt  // 'cursorlineopt'
   char_u      *wo_cc;
 # define w_p_cc w_onebuf_opt.wo_cc      // 'colorcolumn'
+  char_u      *wo_sbr;
+# define w_p_sbr w_onebuf_opt.wo_sbr    // 'showbreak'
   char_u      *wo_stl;
 #define w_p_stl w_onebuf_opt.wo_stl     // 'statusline'
   int wo_scb;