patch 8.2.2319: "exptype_T" can be read as "expected type"

Problem:    "exptype_T" can be read as "expected type".
Solution:   Rename to "exprtype_T", expression type.
diff --git a/src/structs.h b/src/structs.h
index 3324b06..9d1f821 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -4029,7 +4029,7 @@
     EXPR_MULT,		// *
     EXPR_DIV,		// /
     EXPR_REM,		// %
-} exptype_T;
+} exprtype_T;
 
 /*
  * Structure used for reading in json_decode().