vim-patch:8.2.0674: some source files are too big (#19959)

Problem:    Some source files are too big.
Solution:   Move text formatting functions to a new file. (Yegappan
            Lakshmanan, closes vim/vim#6021)
11abd09521

Cherry-pick set_can_cindent() from patch 8.1.2062.
Cherry-pick global old_indent from patch 8.2.2127.

src/nvim/globals.h

@@ -559,6 +559,8 @@ EXTERN bool can_si INIT(= false);
 // one indent will be removed.
 EXTERN bool can_si_back INIT(= false);
 
+EXTERN int old_indent INIT(= 0);  ///< for ^^D command in insert mode
+
 // w_cursor before formatting text.
 EXTERN pos_T saved_cursor INIT(= { 0, 0, 0 });