patch 9.0.0977: it is not easy to see what client-server commands are doing

Problem:    It is not easy to see what client-server commands are doing.
Solution:   Add channel log messages if ch_log() is available.  Move the
            channel logging and make it available with the +eval feature.

src/Makefile

@@ -1531,6 +1531,7 @@ BASIC_SRC = \
 	json.c \
 	list.c \
 	locale.c \
+	logfile.c \
 	main.c \
 	map.c \
 	mark.c \
@@ -1690,6 +1691,7 @@ OBJ_COMMON = \
 	objects/insexpand.o \
 	objects/list.o \
 	objects/locale.o \
+	objects/logfile.o \
 	objects/map.o \
 	objects/mark.o \
 	objects/match.o \
@@ -1874,6 +1876,7 @@ PRO_AUTO = \
 	json.pro \
 	list.pro \
 	locale.pro \
+	logfile.pro \
 	main.pro \
 	map.pro \
 	mark.pro \
@@ -3306,6 +3309,9 @@ objects/list.o: list.c
 objects/locale.o: locale.c
 	$(CCC) -o $@ locale.c
 
+objects/logfile.o: logfile.c
+	$(CCC) -o $@ logfile.c
+
 objects/main.o: main.c
 	$(CCC) -o $@ main.c
 
@@ -3897,6 +3903,11 @@ objects/locale.o: locale.c vim.h protodef.h auto/config.h feature.h os_unix.h \
  proto/gui_beval.pro structs.h regexp.h gui.h libvterm/include/vterm.h \
  libvterm/include/vterm_keycodes.h alloc.h ex_cmds.h spell.h proto.h \
  globals.h errors.h
+objects/logfile.o: logfile.c vim.h protodef.h auto/config.h feature.h os_unix.h \
+ auto/osdef.h ascii.h keymap.h termdefs.h macros.h option.h beval.h \
+ proto/gui_beval.pro structs.h regexp.h gui.h libvterm/include/vterm.h \
+ libvterm/include/vterm_keycodes.h alloc.h ex_cmds.h spell.h proto.h \
+ globals.h errors.h
 objects/main.o: main.c vim.h protodef.h auto/config.h feature.h os_unix.h \
  auto/osdef.h ascii.h keymap.h termdefs.h macros.h option.h beval.h \
  proto/gui_beval.pro structs.h regexp.h gui.h libvterm/include/vterm.h \