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

* change

* recognize vector float product and update tests

test/decompiler/reference/engine/debug/debug-sphere_REF.gc

@@ -83,8 +83,7 @@
      )
     )
    )
-  (let ((v0-10 0))
-   )
+  0
   (none)
   )
 
@@ -131,8 +130,7 @@
      (add-debug-line #t arg0 s4-0 s2-0 arg3 #f (the-as rgba -1))
      )
     )
-   (let ((v0-2 0))
-    )
+   0
    (none)
    )
   )