fix(paste): improve repeating of pasted text (#30438)

- Fixes 'autoindent' being applied during redo.
- Makes redoing a large paste significantly faster.
- Stores pasted text in the register being recorded.

Fix #28561

src/nvim/keycodes.h

@@ -380,6 +380,10 @@ enum key_extra {
 #define K_KENTER        TERMCAP2KEY('K', 'A')   // keypad Enter
 #define K_KPOINT        TERMCAP2KEY('K', 'B')   // keypad . or ,
 
+// Delimits pasted text (to repeat nvim_paste). Internal-only, not sent by UIs.
+#define K_PASTE_START   TERMCAP2KEY('P', 'S')   // paste start
+#define K_PASTE_END     TERMCAP2KEY('P', 'E')   // paste end
+
 #define K_K0            TERMCAP2KEY('K', 'C')   // keypad 0
 #define K_K1            TERMCAP2KEY('K', 'D')   // keypad 1
 #define K_K2            TERMCAP2KEY('K', 'E')   // keypad 2