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/options.lua

@@ -2175,7 +2175,7 @@ return {
     {
       full_name='showbreak', abbreviation='sbr',
       short_desc=N_("string to use at the start of wrapped lines"),
-      type='string', scope={'global'},
+      type='string', scope={'global', 'window'},
       redraw={'all_windows'},
       varname='p_sbr',
       defaults={if_true=""}