patch 9.0.1710: scrolloff options work slightly different

Problem: sidescrolloff and scrolloff options work slightly
         different than other global-local options
Solution: Make it behave consistent for all global-local options

It was noticed, that sidescrolloff and scrolloff options behave
differently in comparison to other global-local window options like
'listchars'

So make those two behave like other global-local options. Also add some
extra documentation for a few special local-window options.

Add a few tests to make sure all global-local window options behave
similar

closes: #12956
closes: #12643

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/option.c b/src/option.c
index 3050dbc..a6d73d2 100644
--- a/src/option.c
+++ b/src/option.c
@@ -6652,6 +6652,8 @@
     to->wo_sms = from->wo_sms;
     to->wo_crb = from->wo_crb;
     to->wo_crb_save = from->wo_crb_save;
+    to->wo_siso = from->wo_siso;
+    to->wo_so = from->wo_so;
 #ifdef FEAT_SPELL
     to->wo_spell = from->wo_spell;
 #endif