docs: add clipboard copy Fiddle example

[RikTheunis]

Description of Change

Refs #20442

Adds the clipboard copy example from electron-api-demos into a runnable Fiddle example.

Gist link to Fiddle (same as code submitted in this PR): https://gist.github.com/263e01f09c1cb44da8d8bf28f2f726ce

Checklist

• PR description included and stakeholders cc'd
• standard linter passes
• PR title follows semantic commit guidelines
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: no-notes

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[codebytere]

@RikTheunis Please merge this into #20445, as they're tightly coupled.

[RikTheunis]

I sure can @codebytere. Should I take other sections of the electron-api-demos together as well as @erickzhao in #20442 said to open a new pull request for each demo?

[erickzhao]

@RikTheunis thinking more about it, I think it'd be reasonable to make 1 PR for a set of demos that are tightly coupled as said above by @codebytere, to make it easier to give feedback and keep track of PRs.

I'll amend the original issue body to clarify.

[RikTheunis]

Closing as changes are merged into #20445.