MM-8867

Create proper getter/setter for CSS::Inliner::TreeBuilder "relaxed" parsing property

Add new method "_validate_html" to report back corrections that TreeBuilder is performing
to make a tree parseable:
* Runs by default, can be skipped over by enabling relaxed parsing. IE does *not* run when relaxed.
* Multiple html, head and body tags all will now generate an warning within the content warnings array.
* Find style tags within body content that are not going to be processed, generate a warning
* Refactor unexpected "link" tags within content, now generate a warning instead of die. RT84513

Convert spurious double quotes to single quotes throughout Inliner.pm

Fix up spacing within method calls throughout Inliner.pm

Remove spurious () within stacked method calls, they make the code harder to read in my opinion.