REFACTOR canonical creation to utilize MetaComponents method

[muskie9]

Current implementation uses the MetaTags() extension method to alter the meta string. Alternatively, it's more reliable to use the MetaComponents() extension method as the meta tags are in an array, allowing for more consistent structure and easier, more reliable alterations to the metadata.

Similar update made in silverstripe/silverstripe-cms#2637

The underlying issue with the current implementation lies in VirtualPage which currently applies a canonical url to the CopyContentFrom page. The pull request noted above moves the canonical creation into MetaComponents() which should allow for a simple detection of an array key vs a regular expression of some type to prevent duplicate canonical tag generation in the case of VirtualPage (or any other custom page types that apply a canonical tag).