Add node pattern methods to handle dependency audits in a better way

[GauthamGoli]

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#569 and #2662
RuboCop has pattern searching macros which simplify searching/matching nodes in AST.
Found documentation for same in the source of node_pattern.rb

This PR updates depends_on audits to use such pattern matching methods, so code becomes more readable and also fixes bug in previous code which wasn't detecting dependencies.

(there is however one edge case where the value of a depends_on hash is an array, I know how exactly to implement that and will deal with that later)

Edit: How did I derive those patterns? By running the below commands and looking at the AST.
$ ruby-parse -e 'depends_on :x11 => optional'
$ ruby-parse -e 'depends_on "readline" => :recommended'

cc @ilovezfs

[MikeMcQuaid]

One question but otherwise: great work here 👍

[MikeMcQuaid]

Worth using EOS or EOS.undent here?

[GauthamGoli]

Yeah.

[MikeMcQuaid]

Thanks again @GauthamGoli!