Conversion between bool[N] and bits[N] should allow control over ordering

### What's hard to do? (limit 100 words)

In XLS, we have a distinction between an array of bools `bool[N]` (i.e. `bits[1][N]`) and a packed bit vector `bits[N]`. Oftentimes, you may choose to write one or the other depending on convenience (e.g. arrays support map, bits support and/or reduce). But in these cases, the order of indices is normally fixed regardless of whether we write it as one version or the other.

stdlib provides `convert_to_bools_lsb0` and `convert_to_bits_msb0` to convert between the two, but it'd be cleaner to have that ordering user-specified.

### Current best alternative workaround (limit 100 words)

You can use `rev` or `array_rev` before or after the conversion functions, to undo the reversing.

### Your view of the "best case XLS enhancement" (limit 100 words)

Provide APIs to convert between the two without extraneous reversing.