text: Title: Option to include all tags and attrs in LinkExtractor with specified exclusions
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  ## Summary
  
  Add the option to the LinkExtractor class to consider all tags and attributes (e.g. if you pass `None` then consider all tags/attributes), and `deny_tags` and `deny_attrs` arguments or similar so you can additionally consider all tags and attributes with the exception of those explicitly passed. 
  
  ## Motivation
  
  It allows adopting a strategy of extracting all links by default and then specifically excluding the tags and attributes you don't want considered. Currently, it seems the user has to figure out all the specific tags and attributes where they're desired links appear and explicitly pass them to `tags` and `attrs` to have them considered.
  
  ## Describe alternatives you've considered
  
  For including all tags, you could use the Selector class instead of LinkExtractor and select all e.g. `href` attributes regardless of which tag they appear in, e.g. `response.xpath('//@href')`. Using Selector results in losing the various convenient arguments in LinkExtractor and requires manually processing them with regex etc instead, and it requires manually converting relative links into absolute links when you want to use regexes that match the entire URL whereas LinkExtractor already handles that automatically.
  
  ## Additional context
  
  Any additional information about the feature request here.
  