Don't reject types directly on AST (#19407)

Instead of rejecting type expressions based on node kind,
evaluate the expression as a type.
This is already the behavior for call results, and it has its own error
for non-types, which is the same error you would normally get
with 2 words swapped.

tests/types/tnontype.nim

@@ -0,0 +1,9 @@
+discard """
+  errormsg: "expected type, but got: 3"
+"""
+
+type
+  Foo = (block:
+    int)
+  
+  Bar = 3