fix. Stylus button press changes tool to Eraser but do not erase.

[QubaB]

Some styluses do not send move events when button is pressed. So Eraser do not work.

This change allows switch to eraser by pressing and releasing stylus button (no more holding button), then erasing items work.

Creates new preference, which can change default behavior of pressing button when pen is above screen.

Solves issue saber-notes#1410

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 37.50000% with 15 lines in your changes missing coverage. Please review.

Project coverage is 47.15%. Comparing base (7d60459) to head (04e94e0).

Files with missing lines	Patch %	Lines
lib/pages/editor/editor.dart	16.66%	15 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1428      +/-   ##
==========================================
- Coverage   47.15%   47.15%   -0.01%     
==========================================
  Files         114      114              
  Lines        9002     9018      +16     
==========================================
+ Hits         4245     4252       +7     
- Misses       4757     4766       +9     

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