[5.3] Fix blade parent keyword escaping

[Ruby184]

This PR is fix for issue #10068 and it's trying to properly handle @parent keywords in Blade sections and ensure proper section extending. The solution is hardly based on previously reverted commit #10122 with a few tweaks.

TODO list:

• Fix original issue [5.1] [5.3] @parent tag is not escaping #10068.
• Add test to ensure @parent keyword is properly handled.
• Edit test for multiple section extending to ensure we will not introduce bugs like @parent totally breaks since 5.1.13 #10156.
• Fix @append behaviour to properly handle parent marks.
• Add tests for section appending.
• Add tests for section overwriting.
• Confirmation from @abhimanyusharma003 @parent keyword is properly escaped.
• Confirmation form @atmediauk this fix is working as expected and has no side effects for him.

Thank you guys. Special thanks to @mspiderv for helping me with figuring out how to fix it and @dmgawel for previous try to fix this issue.

[taylorotwell]

What is the difference between $parentMarks and $parentMarksLast?

[taylorotwell]

Closing pending lack of activity.