Remove mention attribute from selection when selection is at start of…

[jodator]

… parent block.

Suggested merge commit message (convention)

Fix: Remove mention attribute from selection when selection is at the beginning of a parent block. Closes ckeditor/ckeditor5#4663.

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Additional information

• Quit quick fix - the selection set attribute from a node after if it is placed at the begining of a paragraph:

<p>[]<$text mention={}>@foo</$text>

while in such scenario is not:

<p>bar []<$text mention={}>@foo</$text>