Make exclusion list more specific for Magento template files

[fredden]

When working with a website that we have inherited from another agency, I noticed that the Generic.PHP.DisallowShortOpenTag rule was applying to *.php files, but not to *.phtml files. After some investigation, I found that the <exclude-pattern> directive was applying too broadly. When a sniff is in both standards, this <exclude-pattern> rule meant that it would only apply to PHP files, not Magento2 template files.

I made a list of all overlapping sniffs (ie, those in both the Youwe and Magento2 standards), and then included only those that made sense to not apply to Magento template files in the exclude list. To see the sniffs included in these standards, one can run vendor/bin/phpcs -e --standard=Youwe and vendor/bin/phpcs -e --standard=Magento2.

Some examples of a sniffs not marked for exclusion here are:

• GlobalPhpUnit.Coverage.CoversTag - we should not be defining any PHPUnit test classes/methods in template files, so this rule should never match anything anyway.
• PSR12.Classes.OpeningBraceSpace - no classes should be declared in template files, so this rule should never match anything anyway.
• Squiz.WhiteSpace.CastSpacing - cast syntax should be uniform in all files scanned, not just .php files.

This is a follow-up to #5 and #10.

[leonhelmus]

This seems like a good addition thanks @fredden !