Provide a replication operator for arrays/bits

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

Create arrays and bit vectors with replicated patterns. SystemVerilog provides the replication operator which works on both, so you can do stuff like:

```
int n[1:2][1:6] = '{2{'{3{4, 5}}}};
```

which is equivalent to:

```
'{'{4,5,4,5,4,5},'{4,5,4,5,4,5}}
```

Similarly, you can do:

```
{4{4'b1010, 4'b1001}}
```

which is equivalent to

`32'b10101001101010011010100110101001`

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

You could write for loops to do `update` and `bit_slice_update`. Or just copy-paste manually.

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

Support this in DSLX.