feat: show magnifier when dragging the handlers

[LucasXu0]

y.mp4

[codecov]

Codecov Report

Attention: 17 lines in your changes are missing coverage. Please review.

Comparison is base (2ece948) 78.87% compared to head (ef6e484) 78.78%.

Files	Patch %	Lines
...component/service/selection/mobile_magnifiter.dart	0.00%	10 Missing ⚠️
...nt/service/selection/mobile_selection_service.dart	61.53%	5 Missing ⚠️
...or_component/service/selection_service_widget.dart	0.00%	1 Missing ⚠️
...bile_floating_toolbar/mobile_floating_toolbar.dart	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #601      +/-   ##
==========================================
- Coverage   78.87%   78.78%   -0.10%     
==========================================
  Files         289      290       +1     
  Lines       12526    12551      +25     
==========================================
+ Hits         9880     9888       +8     
- Misses       2646     2663      +17     

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