default: enable 'langnoremap'. #2853

Re: https://github.com/neovim/neovim/issues/2676

runtime/doc/options.txt

@@ -4123,7 +4123,7 @@ A jump table for the options with a short description can be found at |Q_op|.
 <	Warning: This deletes all menus that you defined yourself!
 
 					*'langnoremap'* *'lnr'*
-'langnoremap' 'lnr'	boolean (default off)
+'langnoremap' 'lnr'	boolean (default on)
 			global
 	When on, setting 'langmap' does not apply to characters resulting from
 	a mapping.  This basically means, if you noticed that setting

runtime/doc/vim_diff.txt

@@ -33,6 +33,7 @@ these differences.
 - 'backspace' defaults to "indent,eol,start"
 - 'encoding' defaults to "utf-8"
 - 'formatoptions' defaults to "tcqj"
+- 'langnoremap' is set by default
 - 'mouse' defaults to "a"
 - 'nocompatible' is always set
 - 'nrformats' defaults to "hex"

src/nvim/option.c

@@ -1013,9 +1013,9 @@ static vimoption_T
   {"langmenu",    "lm",   P_STRING|P_VI_DEF|P_NFNAME,
    (char_u *)&p_lm, PV_NONE,
    {(char_u *)"", (char_u *)0L} SCRIPTID_INIT},
-  {"langnoremap", "lnr",  P_BOOL|P_VI_DEF,
+  {"langnoremap", "lnr",  P_BOOL,
    (char_u *)&p_lnr, PV_NONE,
-   {(char_u *)FALSE, (char_u *)0L} SCRIPTID_INIT},
+   {(char_u *)FALSE, (char_u *)TRUE} SCRIPTID_INIT},
   {"laststatus",  "ls",   P_NUM|P_VI_DEF|P_RALL,
    (char_u *)&p_ls, PV_NONE,
    {(char_u *)1L, (char_u *)0L} SCRIPTID_INIT},