vim-patch:8.2.2388: no easy way to get the maximum or mininum number value

Problem:    No easy way to get the maximum or mininum number value.
Solution:   Add v:numbermax and v:numbermin.
57d5a01cb4

src/nvim/eval.h

@@ -142,6 +142,8 @@ typedef enum {
     VV_FALSE,
     VV_TRUE,
     VV_NULL,
+    VV_NUMBERMAX,
+    VV_NUMBERMIN,
     VV_NUMBERSIZE,
     VV_VIM_DID_ENTER,
     VV_TESTING,