feat: Open text assets in code editor

[kof]

What changed

• open every textual asset type from the upload registry in an editable CodeMirror dialog
• select installed CodeMirror language support by MIME type and use plain text editing as the fallback
• support txt, csv, md, js, css, json, html, xml, and svg without adding asset-specific language branches to the shared editor
• keep the canvas mounted and interactive behind the dialog
• persist edits on blur, Cmd/Ctrl+S, or Cmd/Ctrl+Enter through the asset replacement pipeline
• preserve folder and description metadata and repoint supported asset references
• clean up failed replacement uploads instead of leaving orphan assets

Impact

Users can open, edit, and persist all text-based upload formats directly in the builder without replacing or reloading the canvas. New text/* upload types will automatically become editable as plain text; installed syntax support is selected by MIME type.

Validation

• pnpm --filter @webstudio-is/builder test -- app/builder/features/text-file-editor/text-file-utils.test.ts app/builder/shared/assets/replace-asset.test.ts app/builder/shared/asset-manager/asset-manager.test.tsx
• pnpm --filter @webstudio-is/builder typecheck
• pnpm exec oxlint --deny-warnings <changed files>
• pnpm exec oxfmt --check <changed files>
• git diff --check
• verified the running dev server applied the changes through Vite HMR

Ref #5824