fix: creating document from slash menu leaves text behind

[LucasXu0]

closes AppFlowy-IO/AppFlowy#6865

Add a new parameter to enable deletion of keywords before inserting the new block.

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 3 lines in your changes missing coverage. Please review.

Project coverage is 72.19%. Comparing base (bf9d7e9) to head (df825cd).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...c/editor/selection_menu/selection_menu_widget.dart	62.50%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #980   +/-   ##
=======================================
  Coverage   72.19%   72.19%           
=======================================
  Files         318      318           
  Lines       15144    15147    +3     
=======================================
+ Hits        10933    10936    +3     
  Misses       4211     4211           

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