[Feature request] Extend a monadic idiom u&.(m&{) to dyadic valence

An idiom `u&.(m&{)` is monadic only implementing:
```j
m}&y u m&{ y           NB. u&.(m&{) y
```
I propose to extend it to support dyadic application implementing:
```j
m}&y (m&{ x) u m&{ y    NB. x u&.(m&{) y
```

That is, to make an idiom `u&.(m&{)` ambivalent.