patch 8.1.2057: the screen.c file is much too big

Problem:    The screen.c file is much too big.
Solution:   Split it in three parts. (Yegappan Lakshmanan, closes #4943)
diff --git a/src/Makefile b/src/Makefile
index c89fdb1..0bfc92d 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -1593,6 +1593,8 @@
 	dict.c \
 	diff.c \
 	digraph.c \
+	drawline.c \
+	drawscreen.c \
 	edit.c \
 	eval.c \
 	evalbuffer.c \
@@ -1727,6 +1729,8 @@
 	objects/dict.o \
 	objects/diff.o \
 	objects/digraph.o \
+	objects/drawline.o \
+	objects/drawscreen.o \
 	objects/edit.o \
 	objects/eval.o \
 	objects/evalbuffer.o \
@@ -1874,6 +1878,8 @@
 	dict.pro \
 	diff.pro \
 	digraph.pro \
+	drawline.pro \
+	drawscreen.pro \
 	edit.pro \
 	eval.pro \
 	evalbuffer.pro \
@@ -3083,6 +3089,12 @@
 objects/digraph.o: digraph.c
 	$(CCC) -o $@ digraph.c
 
+objects/drawline.o: drawline.c
+	$(CCC) -o $@ drawline.c
+
+objects/drawscreen.o: drawscreen.c
+	$(CCC) -o $@ drawscreen.c
+
 objects/edit.o: edit.c
 	$(CCC) -o $@ edit.c
 
@@ -3613,6 +3625,14 @@
  auto/osdef.h ascii.h keymap.h term.h macros.h option.h beval.h \
  proto/gui_beval.pro structs.h regexp.h gui.h alloc.h ex_cmds.h spell.h \
  proto.h globals.h
+objects/drawline.o: drawline.c vim.h protodef.h auto/config.h feature.h os_unix.h \
+ auto/osdef.h ascii.h keymap.h term.h macros.h option.h beval.h \
+ proto/gui_beval.pro structs.h regexp.h gui.h alloc.h ex_cmds.h spell.h \
+ proto.h globals.h
+objects/drawscreen.o: drawscreen.c vim.h protodef.h auto/config.h feature.h os_unix.h \
+ auto/osdef.h ascii.h keymap.h term.h macros.h option.h beval.h \
+ proto/gui_beval.pro structs.h regexp.h gui.h alloc.h ex_cmds.h spell.h \
+ proto.h globals.h
 objects/edit.o: edit.c vim.h protodef.h auto/config.h feature.h os_unix.h \
  auto/osdef.h ascii.h keymap.h term.h macros.h option.h beval.h \
  proto/gui_beval.pro structs.h regexp.h gui.h alloc.h ex_cmds.h spell.h \