docs: update defineCustomElements(window) to defineCustomElements()

[peterpeterparker]

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With the new version of Stencil, which we have upgraded in all our components, passing window to defineCustomElements(window) isn't mandatory anymore and is even more convenient without, as prerendering, like with Gatsby, might not have access to window.

That's why the goal of this task is to replace all defineCustomElements(window) in the documentation (docs project) with defineCustomElements().