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.
diff --git a/src/evalvars.c b/src/evalvars.c
index 1799531..dfc8e63 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -122,6 +122,8 @@
     {VV_NAME("true",		 VAR_BOOL), VV_RO},
     {VV_NAME("none",		 VAR_SPECIAL), VV_RO},
     {VV_NAME("null",		 VAR_SPECIAL), VV_RO},
+    {VV_NAME("numbermax",	 VAR_NUMBER), VV_RO},
+    {VV_NAME("numbermin",	 VAR_NUMBER), VV_RO},
     {VV_NAME("numbersize",	 VAR_NUMBER), VV_RO},
     {VV_NAME("vim_did_enter",	 VAR_NUMBER), VV_RO},
     {VV_NAME("testing",		 VAR_NUMBER), 0},
@@ -228,6 +230,8 @@
     set_vim_var_nr(VV_TRUE, VVAL_TRUE);
     set_vim_var_nr(VV_NONE, VVAL_NONE);
     set_vim_var_nr(VV_NULL, VVAL_NULL);
+    set_vim_var_nr(VV_NUMBERMAX, VARNUM_MAX);
+    set_vim_var_nr(VV_NUMBERMIN, VARNUM_MIN);
     set_vim_var_nr(VV_NUMBERSIZE, sizeof(varnumber_T) * 8);
 
     set_vim_var_nr(VV_TYPE_NUMBER,  VAR_TYPE_NUMBER);