patch 8.1.1210: support for user commands is spread out

Problem:    Support for user commands is spread out. No good reason to make
            user commands optional.
Solution:   Move user command support to usercmd.c.  Always enable the
            user_commands feature.
diff --git a/Filelist b/Filelist
index fc6374b..a6cc76c 100644
--- a/Filelist
+++ b/Filelist
@@ -98,6 +98,7 @@
 		src/textprop.c \
 		src/ui.c \
 		src/undo.c \
+		src/usercmd.c \
 		src/userfunc.c \
 		src/version.c \
 		src/version.h \
@@ -212,6 +213,7 @@
 		src/proto/textprop.pro \
 		src/proto/ui.pro \
 		src/proto/undo.pro \
+		src/proto/usercmd.pro \
 		src/proto/userfunc.pro \
 		src/proto/version.pro \
 		src/proto/winclip.pro \