Improve "Straighten UV" performance

[Fak3]

System Information

• OS: Linux
• Blender version: 2.83
• Add-on version: Git master

O the file with many vertices, "Straighten UV" takes more than 20 minutes to complete, and in the end it throws an error "All UVs are not sparated"

For example this blend file: https://drive.google.com/file/d/1U2MhaL0f6Ry6SB4c0YYDyIG00xbzk9qf/view?usp=sharing

• in the uv editor, open N menu, there open the magic uv tab -> UV manipulation -> Align UV
• Select some faces
• Click "Straighten"

[nutti]

@Fak3

I will refactor this feature because of many bugs.

Thanks for lots of testing this add-on. It's very helpful because I didn't use this add-on in the environment with many vertices.