feat: custom slice function

[LucasXu0]

Allow the developer to customize the delta slice function.

One use case is skipping formatting for inline code of the subsequently input text with French IME.

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 3 lines in your changes missing coverage. Please review.

Project coverage is 72.03%. Comparing base (8ae43d4) to head (a0d9400).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/src/core/document/text_delta.dart	83.33%	2 Missing ⚠️
...rvice/ime/delta_input_on_non_text_update_impl.dart	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #935      +/-   ##
==========================================
+ Coverage   72.02%   72.03%   +0.01%     
==========================================
  Files         318      318              
  Lines       15036    15046      +10     
==========================================
+ Hits        10829    10838       +9     
- Misses       4207     4208       +1     

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