Refactor: Resolve repeated code between server's previewGeneration.js and client's EmbedFrame.jsx

[Shyam-Raghuwanshi]

Fixes #2805

Changes:

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123

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[raclim]

Thanks for your work on this!

I think that although what's here so far does resolve the issue of repeated code between the two files, this doesn't address some of the other tasks listed in the issue (i.e "Add explanatory comments in the code, Add unit tests, Make improvements to the code itself...") that would help implement a more thorough, long-term solution.

Due to the number of PRs we have at the moment, I'm going to close this one for now. I'm sorry that we couldn't get this in yet, but please feel free to reopen this PR and update it with the needed changes, thanks!