fix(api): nvim_set_option_value for global-local options

global-local window options need to be handled specially. When `win` is
given but `scope` is not, then we want to set the local version of the
option but not the global one, therefore we need to force
`scope='local'`.

Note this does not apply to window-local only options (e.g. 'number')

Example:

   nvim_set_option_value('scrolloff', 10, {})       -- global-local window option; set global value
   nvim_set_option_value('scrolloff', 20, {win=0})  -- global-local window option; set local value
   nvim_set_option_value('number', true, {})        -- local window option

is now equivalent to:

   nvim_set_option_value('scrolloff', 10, {})
   nvim_set_option_value('scrolloff', 20, {win=0, scope='local'})  -- changed from before
   nvim_set_option_value('number', true, {win=0})                  -- unchanged from before

Only the global-local option with a `win` provided gets forced to local
scope.

src/nvim/api/options.c

@@ -156,6 +156,19 @@ void nvim_set_option_value(String name, Object value, Dict(option) *opts, Error
     return;
   }
 
+  // If:
+  // - window id is provided
+  // - scope is not provided
+  // - option is global or local to window (global-local)
+  //
+  // Then force scope to local since we don't want to change the global option
+  if (opt_type == SREQ_WIN && scope == 0) {
+    int flags = get_option_value_strict(name.data, NULL, NULL, opt_type, to);
+    if (flags & SOPT_GLOBAL) {
+      scope = OPT_LOCAL;
+    }
+  }
+
   long numval = 0;
   char *stringval = NULL;
 
@@ -454,11 +467,12 @@ void set_option_to(uint64_t channel_id, void *to, int type, String name, Object
     stringval = value.data.string.data;
   }
 
-  WITH_SCRIPT_CONTEXT(channel_id, {
-    const int opt_flags = (type == SREQ_WIN && !(flags & SOPT_GLOBAL))
-                          ? 0 : (type == SREQ_GLOBAL)
-                                ? OPT_GLOBAL : OPT_LOCAL;
+  // For global-win-local options -> setlocal
+  // For        win-local options -> setglobal and setlocal (opt_flags == 0)
+  const int opt_flags = (type == SREQ_WIN && !(flags & SOPT_GLOBAL)) ? 0 :
+                        (type == SREQ_GLOBAL)                        ? OPT_GLOBAL : OPT_LOCAL;
 
+  WITH_SCRIPT_CONTEXT(channel_id, {
     access_option_value_for(name.data, &numval, &stringval, opt_flags, type, to, false, err);
   });
 }

test/functional/lua/vim_spec.lua

@@ -1424,6 +1424,13 @@ describe('lua stdlib', function()
     vim.wo[1000].cole = 0
     ]]
     eq(0, funcs.luaeval "vim.wo[1000].cole")
+
+    -- Can handle global-local values
+    exec_lua [[vim.o.scrolloff = 100]]
+    exec_lua [[vim.wo.scrolloff = 200]]
+    eq(200, funcs.luaeval "vim.wo.scrolloff")
+    exec_lua [[vim.wo.scrolloff = -1]]
+    eq(100, funcs.luaeval "vim.wo.scrolloff")
   end)
 
   describe('vim.opt', function()