patch 8.1.2000: plugin cannot get the current IME status

Problem:    Plugin cannot get the current IME status.
Solution:   Add the getimstatus() function. (closes #4904)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 0aa8fbf..b2ab63d 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -507,6 +507,7 @@
     {"getfsize",	1, 1, FEARG_1,	  f_getfsize},
     {"getftime",	1, 1, FEARG_1,	  f_getftime},
     {"getftype",	1, 1, FEARG_1,	  f_getftype},
+    {"getimstatus",	0, 0, 0,	  f_getimstatus},
     {"getjumplist",	0, 2, FEARG_1,	  f_getjumplist},
     {"getline",		1, 2, FEARG_1,	  f_getline},
     {"getloclist",	1, 2, 0,	  f_getloclist},