Post-Vue-dashboard file moves

[jcushman]

This PR makes a bunch of cleanup moves now that we're moving the Vue dashboard out of a developer flag. These tend to step on file history, so I'm doing them in one big batch in the hopes of getting that out of the way:

• Move everything out of the developer-playground flag. We're keeping the flag itself for potential use later.
• Re-indent the new Vue files in frontend/ with two spaces, which is what we generally use for HTML/CSS/JS. (It would make sense at some point to adopt ESLint and Prettier, but I just did a quick effort with Pycharm for now since the files are moving anyway, in the hopes of reducing the diff size for that effort later.)
• Delete all of the now-unused javascript from the old create page.
• Move the frontend/ folder to static/frontend/. In working with Vite I found that it was hard to get both developer and production builds working with the right paths when we had Vue and CSS in different static folders.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 69.73%. Comparing base (f3d5fd4) to head (62019e9). Report is 6 commits behind head on develop.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #3619 +/- ## ======================================== Coverage 69.73% 69.73% ======================================== Files 54 54 Lines 7326 7326 ======================================== Hits 5109 5109 Misses 2217 2217 ```

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[sentry-io[bot]]

Suspect Issues

This pull request was deployed and Sentry observed the following issues:

• ‼️ TypeError: undefined is not an object (evaluating '_babel_runtime_corejs3_core_js_stable_instance_includes__... <anonymous>(frontend/components/Toast) View Issue
• ‼️ TypeError: Cannot read properties of null (reading 'status') _callee$(frontend/components/UploadForm) View Issue
• ‼️ TypeError: response is null _callee$(frontend/components/CreateLink) View Issue
• ‼️ TypeError: Cannot read properties of null (reading 'state') selectSavedFolder(frontend/components/JSTree) View Issue
• ‼️ TypeError: Cannot read properties of null (reading 'state') selectSavedFolder(frontend/components/JSTree) View Issue

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