patch 8.2.2188: Vim9: crash when calling global function from :def function

Problem:    Vim9: crash when calling global function from :def function.
Solution:   Set the outer context.  Define the partial for the context on the
            original function. Use a refcount to keep track of which ufunc is
            using a dfunc. (closes #7525)

src/structs.h

@@ -1363,6 +1363,7 @@ typedef struct jsonq_S jsonq_T;
 typedef struct cbq_S cbq_T;
 typedef struct channel_S channel_T;
 typedef struct cctx_S cctx_T;
+typedef struct ectx_S ectx_T;
 
 typedef enum
 {