## Summary
Split mask editor structure into smaller files
## Changes
This PR is a prerequisite step for [the issue - refactoring the mask
editor using
Vue](https://github.com/Comfy-Org/ComfyUI_frontend/issues/5956). It
splits the current monolithic maskeditor.ts (about 5700 lines) into
separate files; otherwise, the original single file would be very
difficult to analyze or maintain.
This PR itself does not introduce any Vue, nor should it have any
functional changes or modifications. It's purely a code-level split,
with all related files placed in the maskeditor folder.
The original maskeditor.ts has been renamed to maskeditor.ts.backup for
future reference.
## Review Focus
Since this PR is only for splitting purposes, all logic remains
consistent with the original. Therefore, for any reviewer: any code
logic improvements should happen in the subsequent Vue-based
refactoring, not in this PR.
Following this PR, I will perform a Vue-based refactoring of the mask
editor to align with the frontend's overall Vue architecture and provide
better cloud-related support.
┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6308-refactor-Split-mask-editor-into-smaller-files-2986d73d36508131937dd43e465a47bd)
by [Unito](https://www.unito.io)
