Generating All-In-One LaTex File for Journal Submission

Recently I need to submit to a journal that does NOT accept the final PDF but requires all LaTex sources so that they can compile the PDF on their own. Given that any LaTex projects with reasonable size would have multiple *.tex, *.bib and figure files. It'll be nice to flatten the LaTex project so that we have as few as files to upload. Here is how.

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