Issue 41050 tutorial examples to manifest V3 (#41812)

* Issue 41050 tutorial examples to manifest V3

* Initial full edits on both extension creation walkthroughts

* Apply suggestions from code review

Co-authored-by: Simeon Vincent <svincent@gmail.com>

* additional edits

* Edits to remaining pages

* Apply suggestions from review

Co-authored-by: Rob Wu <rob@robwu.nl>

* Further revisions for feedback

* Changes to reflect example coda updates
Standardizing extension/Webextensions API terminology
Move comments about cross-browser development from end to start of what are extensions article
Miscellaneous edits

* Apply linter suggestions

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Rob Wu <rob@robwu.nl>

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Co-authored-by: Simeon Vincent <svincent@gmail.com>
Co-authored-by: Rob Wu <rob@robwu.nl>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>