[SeoJCalive]

What does this change?

Part of #806. Follow-up to #1036, as asked in the review: the group editor's add list now follows the field switches, like the toolbar editor's Available presets.

• Add list: a preset whose target format belongs only to turned-off fields isn't offered. It uses the same check as the palette (FormatFields.IsShown), so a format that is also in a field that's on stays (EOT with Fonts off, because it is also in Old formats).
• Members stay: presets already in the group aren't removed or hidden in the editor (rule 7). Removing one from the group doesn't put it back in the add list while its fields are off.

Type of change

• New feature or improvement

How was it tested?

On this branch on top of main at 885e7f62 (with #1036 and #1046).

• dotnet format --verify-no-changes
• Build warnings: 17, the same list as on main, none of them in a file this PR touches.
• dotnet test: the group editor, field switch, toolbar editor and Fields page App tests (30/30). CI covers the rest.
• New test Presets_of_turned_off_fields_are_not_offered_but_members_stay: with Fonts off, a TTF member stays, OTF isn't offered, EOT and PNG are; after removing TTF it isn't offered; with every field on, OTF is offered again.
• Mutation check: without the IsShown filter, the new test fails (Assert.DoesNotContain); with it back, the group editor tests pass.

Screenshots (UI changes)

Korean, Fonts off, the add list opened (rendered headlessly on #1036's head caf5e52f, before #1046, which only changes hover and cursors in this window). Before, TTF follows DWG; after, EOT does, and TTF, OTF, WOFF and WOFF2 are gone (140 → 136 presets).

Before	After

Checklist

• New UI strings are in all src/Filee.App/Assets/i18n/*.json files (none added)
• New third-party code or binaries are listed in THIRD-PARTY-NOTICES.md (none added)
• The PR does one thing (unrelated changes go in a separate PR)

[KnifeLemon]

@SeoJCalive #1036 리뷰에서 말한 그룹 편집기 추가 목록까지 바로 이어서 올려 줘서 고마워요.

• 추가 목록: 툴바 편집기의 사용 가능한 프리셋과 똑같이 FormatFields.IsShown 하나로 걸러서, 두 목록이 서로 어긋날 일이 없어요. 다른 분야에도 속한 EOT는 그대로 나와요.
• 이미 들어 있는 항목: 그대로 남아요(규칙 7). 빼면 꺼진 분야인 동안은 목록에 다시 나오지 않는데, 팔레트와 같은 동작이라 맞아요.
• 시험: 남는 항목, 걸러지는 항목, 다른 분야 덕에 남는 항목, 스위치를 다시 켰을 때까지 다 확인하고, finally로 설정을 되돌려 놓아서 다른 시험에 영향이 없어요.

CI도 모두 초록이라 머지할게요. #806의 남은 부분은 이슈에서 이어서 정리해요.