[progress bar]Imrpove Control process management

[bordoray]

期限: Schedule

• ○○まで

詳細・解決方針: Details

not layer by layer but symbol by symbol or category by category may improve debug management

https://github.com/MIERUNE/qgis-plugin-for-plugx/pull/104#issuecomment-1657945137

iguchi's comment ↓ The problem is:

• to indicate progress, we need "emit" events inside process
• to indicate progress for each symbol-layer, we need "emit" events inside process for it. 　　- but the process is capsulated