[4.0] Keep Script/Style Declarations as an array instead of merge to one string

[Fedik]

Summary of Changes

Keep Script/Style Declarations as an array instead of merge to one string.
For long time JDocument merge all Script/Styles declarations to a single string, which not allow to use it for stuff like type="module" (which has import statement), or micro-data type="application/ld+json", and for other types that get broken when they merged.

This patch introduce a little B.C. (for extensions which use $doc->_script directly) but I think it not very critical, and better we do it now than never.

Additionally after little changes in #25301 this patch will allow to remove specific Script/Styles declarations without parsing whole $doc->_script/_style.

Testing Instructions

Apply the patch and make sure all still works as before.

Documentation Changes Required

This is potential B.C. and need to be described https://docs.joomla.org/Potential_backward_compatibility_issues_in_Joomla_4

The Document::_script, Document::_style store Script/Styles declarations as an array, instead of string.

[wilsonge]

Thanks!

[brianteeman]

See #25788