This PR enforces the usage of platform-based API for file exports ensuring compatibility across web and Desktop apps. This accounts for export flows related to collections (REST/GQL) & environments.

Closes #4332 HFE-578.

What's changed

• The initializeDownloadCollection() helper function is renamed to initializeDownloadFile() and the implementation has been updated to rely on the platform-level APIs instead of the browser-based behaviour. It now returns a promise.
• For exports in general, there'll be a suggested name having the name computed from the URL (based on contents) as a fallback. The platform-level definition under hoppscotch-selfhost-web saveFileWithDialog(), is updated to prioritise the name if supplied.
• The exportAsJSON helper function compiling the export business logic for environments is refactored to leverage the above helper function.
• Minor code refactors aimed at eliminating redundancy to consume existing computed properties, etc and related cleanup.

Notes to reviewers

Please verify all the export flows (individual/bulk at the workspace level) for both the web and Desktop apps.