Highlight ruby debugger lines appropriately

[bostonaholic]

Fixes #16357

The change expands the matching regex to only highlight lines where the debugger is the first word on a line.

The intended behavior is to highlight lines that are calling a ruby debugger. The purpose is to warn developers that might push code to production with a debugger enabled. The change expands the matching regex to only highlight lines where the debugger is the first word on a line.

There are cases in which the current regex is highlighting lines as a false-positive. I first noticed this in my Gemfile when it was highlighting the line below:

gem 'pry-byebug'

Other cases include: commented lines and defined function names that match a known debugger.

See below for cases in which the line should and should not be highlighted.

# frozen_string_literal: true

# This is a test class for ruby debugger highlighting
class Test
  # This line below should not be highlighted
  def byebug
    byebug # this line should be highlighted
    # byebug This comment shouldn't be highlighted

    binding.irb # this line should be highlighted
    # binding.irb this line should not be highlighted

    binding.pry # this line should be highlighted
    # binding.pry this line should not be highlighted
  end
end

Before:

After: