[FIRRTL] Generate filelist for each public module

According to the FIRRTL ABI spec:

> Each public module in a circuit shall produce a filelist that contains the filename of the file containing the public module and any necessary files that define all public or private module files instantiated under it.

Source here: https://github.com/chipsalliance/firrtl-spec/blob/fcd97a59319eab2553afc301d13ccc9af965a2b8/abi.md?plain=1#L48

However, if you have this FIRRTL:

```firrtl
FIRRTL version 4.0.0
circuit Foo :
public module Bar :

public module Foo :
inst bar of Bar
```

And run this command:

```
$ firtool --split-verilog Foo.fir -o out
```

Then in the `out` directory, you'll get `Foo.sv`, `Bar.sv`, and `filelist.f`. The filelist is for module `Foo`, and it contains:

```
$ cat out/filelist.f
Bar.sv
Foo.sv
```

According to the ABI spec, we should get `out/filelist_Foo.f` and `out/filelist_Bar.f`, right?

Possibly related to https://github.com/llvm/circt/issues/6716.

Reproduce the documented firtool command with the provided FIRRTL circuit and inspect the generated files in the output directory. Compare the result with the FIRRTL ABI specification and issue 6716; done means each public module has its own filelist containing its file and required instantiated module files.

Written by the indexing model from the issue text.