[decompiler] clean up vector detection and add vector float product detection (#638)

* change

* recognize vector float product and update tests

test/decompiler/reference/engine/data/art-h_REF.gc

@@ -509,5 +509,4 @@
   )
 
 ;; failed to figure out what this is:
-(let ((v0-37 0))
-  )
+0

test/decompiler/reference/engine/data/res-h_REF.gc

@@ -63,5 +63,4 @@
 (define *res-key-string* (new 'global 'string 64 (the-as string #f)))
 
 ;; failed to figure out what this is:
-(let ((v0-4 0))
-  )
+0