fill_like default eltype should be the one of the fill value

Right now we have the signature
```
fill_like(x::AbstractArray, val, [element_type=eltype(x)], [dims=size(x)]))
```
I think it should be
```
fill_like(x::AbstractArray, val, [element_type=typeof(val)], [dims=size(x)]))
```
instead.

Start by locating the fill_like definition and any existing tests for its default element type. Check how the default is selected when val differs from eltype(x), and verify that the default follows typeof(val) while explicit element_type and dims arguments retain their behavior.

Written by the indexing model from the issue text.