Object Basics: Move array content to "Arrays and Loops" lesson

[MaoShizhong]

Because

The lesson contents on array methods in Object Basics is misplaced and would be better served in the Arrays and Loops lesson instead. This will keep both lessons more focused on relevant topics.

This PR

• Moves all array method content and assignments in "Object Basics" to "Arrays and Loops"
  • "Object Basics" LO/KC amended accordingly.
  • Some restructuring of assignments/lesson bullets to for better flow of topics.
  • Added link to MDN Array docs for reference purposes.
  • Since it would be too much otherwise, some W3Schools array resources were removed in favour of the incoming javascript.info resources.
• Tweaks some verbiage to move away from the idea of "mastering" anything and from the idea of "shorter is better", since code length is just an outcome of any given code and not actually the cause of more readable code.
• Fixes some line breaks for better visuals when rendered on the site, and removes some redundant escape slashes.
• Fixes some nested list indentation to match style guide (3 spaces for child of ordered list)

Issue

Closes #29500

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[MaoShizhong]

Opinion wanted:

With the array method contents now in the Arrays and Loops lesson, I feel like the section order (Arrays -> Loops -> Array method stuff) could flow better if Loops came first, followed by Arrays then the Array method stuff.

The array resources either mention loops or otherwise use looping concepts when demonstrating array methods. Meanwhile, the MDN loops resource (not the other one) only very briefly mention arrays, and not in an array method context, only to use a for..of loop for. I feel like going Loops first would make more sense, perhaps with a tiny note that arrays are just lists of things and we'll cover them in the next section. Feels better than going Arrays and methods first, which naturally include iteration, then introducing loops like they're completely separate.

If agreed, I can open a separate issue for this after this one is complete, and it might mean the lesson could do with renaming to "Loops and Arrays" (which would require a file name change, a link change in Object Basics (only place it's linked), and a change in the website repo for the title).