Align local nav and add breadcrumbs for pages

[outdoor2kode]

Closes #2511

This PR ensures that the page has the correct breadcrumbs. Additionally, it makes the local navigation behave according to the design shown in the image below.

I'm not so sure where the learning pathway term falls, because the term page is already at Level 3 depth, and due to the design, there are no breadcrumbs, so should we follow the behavior of L3 by displaying the term name in the local navigation when scrolling? cc @fcoveram

Default	Scroll

Also, for the L2B part, it will need to have a breadcrumb level value to help with the determination. So I'm going to wait to see if the current method of retrieving that value makes sense.

Screenshots

	Default	Scroll
L3
L2A		Same
		Same
		Same. Note that the link isn't highlighted
		Same. Note that the link isn't highlighted
		Same
L1B	This site doesn't have L1B	-
L1A

[adamwoodnz]

Found another edge case @renintw, freestanding Lessons don't have a Course parent for the breadcrumb. Breadcrumb should probably be Home / Lessons / Lesson Title

[outdoor2kode]

Found another edge case @renintw, freestanding Lessons don't have a Course parent for the breadcrumb. Breadcrumb should probably be Home / Lessons / Lesson Title

Weird, I don't see this issue either in this PR or in #2594

[adamwoodnz]

Found another edge case @renintw, freestanding Lessons don't have a Course parent for the breadcrumb. Breadcrumb should probably be Home / Lessons / Lesson Title

Weird, I don't see this issue either in this PR or in #2594

Try this one https://learn.wordpress.org/lesson/publishing-with-the-block-editor/

[outdoor2kode]

Found another edge case @renintw, freestanding Lessons don't have a Course parent for the breadcrumb. Breadcrumb should probably be Home / Lessons / Lesson Title

Weird, I don't see this issue either in this PR or in #2594

Try this one https://learn.wordpress.org/lesson/publishing-with-the-block-editor/

I think that's the data issue, as other freestanding lessons look fine, though I didn't check all the lessons, there might be some out there. This can be fixed by saving the post again, it's likely that the lesson originally belonged to a course, and that course was deleted but the related data for the lesson is still there.

Open a ticket for it: https://github.com/WordPress/Learn/issues/2644#issue-2394564182

Note: this is the logic where processing the freestanding lessons, for the example raised here, it has a value for lesson_course_id, but the course doesn't exist. That's why I think it originally belonged to a course.