apl: ⊆ partition — mask-driven split (+8)

- apl-partition: new partition where M[i]>M[i-1] (init prev=0);
  continue where M[i]≤prev∧M[i]≠0; drop cells where M[i]=0
- Returns apl-vector of apl-vector parts
- pipeline 140/140

lib/apl/transpile.sx

@@ -97,6 +97,7 @@
       ((= g "∩") apl-intersect)
       ((= g "⊥") apl-decode)
       ((= g "⊤") apl-encode)
+      ((= g "⊆") apl-partition)
       (else (error "no dyadic fn for glyph")))))
 
 (define