FormatParameterMismatch fails when modifiers appear before name

[jcraigk]

Expected behavior

When using the Lint/FormatParameterMismatch cop, I expect it to accept all valid variations of format strings, including those where modifiers appear before the named substitution.

Actual behavior

When running the Lint/FormatParameterMismatch cop, it does not recognize valid format strings where modifiers are supplied before the named parameter.

For example, the following lines produce equivalent output in Ruby v2.6.3 (note the placement of the modifier digit 2 before and after the named substitution):

$ irb
2.6.3 :001 > format('%2<greeting>s', greeting: 'Hello')
 => "Hello"
2.6.3 :002 > format('%<greeting>2s', greeting: 'Hello')
 => "Hello"

The first one produces a Lint/FormatParameterMismatch warning, which is unexpected.

Steps to reproduce the problem

Run the Lint/FormatParameterMismatch cop against the Ruby code format('%2<greeting>s', greeting: 'Hello')

RuboCop version

$ rubocop -V
0.74.0 (using Parser 2.6.3.0, running on ruby 2.6.3 x86_64-darwin17)