cue: add builtins and and or

These allow computing disjunctions and
conjunctions, for instance resulting from
comprehensions.

Change-Id: I1db6566c9114d70017c923e93f1c1d4091085db9
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/1920
Reviewed-by: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Marcel van Lohuizen <mpvl@google.com>
diff --git a/cue/ast.go b/cue/ast.go
index 6d6e8fa..3ff7483 100644
--- a/cue/ast.go
+++ b/cue/ast.go
@@ -345,6 +345,10 @@
 
 			case "len":
 				return lenBuiltin
+			case "and":
+				return andBuiltin
+			case "or":
+				return orBuiltin
 			}
 			if r, ok := predefinedRanges[n.Name]; ok {
 				return r