fix(defaults): keywordprg=:help on Windows #33336

Problem:
As `:h kp` says, the default value for keywordprg
should be ':help' on Windows. It is currently
always ':Man'.

Solution:
Add condition to options.lua which sets keywordprg
to ':help' if running on windows.

(cherry picked from commit 3ebde5ea14)

src/nvim/options.lua

@@ -4789,7 +4789,9 @@ local options = {
     {
       abbreviation = 'kp',
       defaults = {
-        if_true = ':Man',
+        condition = 'MSWIN',
+        if_true = ':help',
+        if_false = ':Man',
         doc = '":Man", Windows: ":help"',
       },
       desc = [=[