patch 8.1.1687: the evalfunc.c file is too big

Problem:    The evalfunc.c file is too big.
Solution:   Move testing support to a separate file.
diff --git a/Filelist b/Filelist
index dfa5307..c3262ef 100644
--- a/Filelist
+++ b/Filelist
@@ -100,6 +100,7 @@
 		src/terminal.c \
 		src/term.h \
 		src/termlib.c \
+		src/testing.c \
 		src/textprop.c \
 		src/ui.c \
 		src/undo.c \
@@ -224,6 +225,7 @@
 		src/proto/term.pro \
 		src/proto/terminal.pro \
 		src/proto/termlib.pro \
+		src/proto/testing.pro \
 		src/proto/textprop.pro \
 		src/proto/ui.pro \
 		src/proto/undo.pro \