FormatParameterMismatch should ignore dynamic widths

[deivid-rodriguez]

$ cat bug.rb 
max_width = 7
id = 58
format('%*d', max_width, id)

$ rubocop bug.rb
Inspecting 1 file
W

Offenses:

bug.rb:3:1: W: Lint/FormatParameterMismatch: Number arguments (2) to format mismatches expected fields (1).
format('%*d', max_width, id)
^^^^^^

1 file inspected, 1 offense detected

This is a hard cop to get right...

[bbatsov]

//cc @edmz

[edmz]

I have been working on these, but they are a bit harder than what I originally thought.

[dreyks]

what about the opposite situation?

v = [1, 2]
format('%d%d', *v)

W: Number arguments (1) to format mismatches expected fields (2).

this should probably be ignored too