Add semgrep rules for file uploader

We have several native input="file" as well as a custom implementations in app/assets/javascripts/vue_shared/components/upload_dropzone/upload_dropzone.vue, app/assets/javascripts/ide/components/new_dropdown/upload.vue && app/assets/javascripts/dropzone_input.js. HAML files do not seem to have file uploaders. Let me know if you see anything missing.

But we do not have an implementation of a GOOD file uploader in GitLab UI. Here is the implementation issue.

Closes #27 (closed)