Fix fixed-angular box regions for polyline

[pford]

Description

• What is implemented or fixed? Mention the linked issue(s), if any. Fixes #1258
• How does this PR solve the issue? Give a brief summary. Reset trim flag, for first region in line segment only. Add computed box (polygon) regions to vector.
• Are there any companion PRs (frontend, protobuf)? No
• Is there anything else that testers should know (e.g. exactly how to reproduce the issue)? Set polyline in widefield image, should be spatial profile for active region.

Checklist

• [x] changelog updated / ~no changelog update needed~
• [x] e2e test passing / added corresponding fix
• [x] ~protobuf updated to the latest dev commit~ / no protobuf update needed
• [x] added reviewers and assignee
• [x] added ZenHub estimate, milestone, and release

[pford]

Needs a formatting pass; otherwise looks fine.

The formatting job (not the check) failed, so I restarted it. No new commits.

[github-actions[bot]]

Package	Line Rate	Health
src.Cache	65%	➖
src.DataStream	52%	➖
src.FileList	67%	➖
src.Frame	50%	➖
src.HttpServer	43%	➖
src.ImageData	28%	❌
src.ImageFitter	89%	✔
src.ImageGenerators	44%	➖
src.ImageStats	76%	✔
src.Logger	44%	➖
src.Main	54%	➖
src.Region	18%	❌
src.Session	29%	❌
src.Table	52%	➖
src.ThreadingManager	87%	✔
src.Timer	85%	✔
src.Util	49%	➖
Summary	38% (6906 / 18266)	❌