Highlight ruby debugger lines appropriately

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.

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

```ruby
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.

```ruby

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
```

CHANGELOG.develop

@@ -34,6 +34,7 @@ the [[file:CHANGELOG.org][CHANGELOG.org]] file.
 * Release 0.300.x
 ** 0.300.0
 *** Hot new feature
+- Highlight ruby debugger lines appropriately
 - Add support for Android emacs.
 - Extensive use of lazy loading of packages and other tricks to reduce Spacemacs
  startup time. In most cases you should see a noticable improvement in load

layers/+lang/ruby/funcs.el

@@ -138,9 +138,9 @@ Called interactively it prompts for a directory."
  "Highlight break point lines."
  (interactive)
  (when ruby-highlight-debugger-keywords
- (highlight-lines-matching-regexp "byebug")
- (highlight-lines-matching-regexp "binding.irb")
- (highlight-lines-matching-regexp "binding.pry")))
+ (highlight-lines-matching-regexp "^\s*byebug")
+ (highlight-lines-matching-regexp "^\s*binding.irb")
+ (highlight-lines-matching-regexp "^\s*binding.pry")))
 
 
 ;; Insert text