patch 9.0.2076: Vim9: No support for type aliases

Problem:  Vim9: No support for type aliases
Solution: Implement :type command

A type definition is giving a name to a type specification.  This also known
type alias.

	:type ListOfStrings = list<string>

The type alias can be used wherever a built-in type can be used.  The type
alias name must start with an upper case character.

closes: #13407

Signed-off-by: Christian Brabandt <cb@256bit.org>
Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
diff --git a/src/json.c b/src/json.c
index e2a0113..66b8bf9 100644
--- a/src/json.c
+++ b/src/json.c
@@ -310,6 +310,7 @@
 	case VAR_INSTR:
 	case VAR_CLASS:
 	case VAR_OBJECT:
+	case VAR_TYPEALIAS:
 	    semsg(_(e_cannot_json_encode_str), vartype_name(val->v_type));
 	    return FAIL;