erl-shell expands zero-arity functions completely: adds the closing parenthesis.

Say you have a module **m** with 3 exported functions:
```
my_func/0
my_func/1
ok_fun/0
```
Then the shell can now tab-completion (-->) this:
```
m:ok_ --> m:ok_fun()
```
Still, old (correct) behaviour is preserved:
```
m:my --> m:my_func(             %% instead of expanding to “m:my_func()”
```

These are the actual changes: https://github.com/fenollp/otp/blob/88753d3c3c0875d8ad6c04fe422559a2f328edda/lib/stdlib/src/edlin_expand.erl#L91-L98
Related tests is mostly this one: https://github.com/fenollp/otp/blob/cdee8ad3b69fb32a550b8711f04b5c5c9818d696/lib/stdlib/test/edlin_expand_SUITE.erl#L85-L86