soffice: Announce actually deleted text on Ctrl+backspace (#15558)
Fixes #15436
Summary of the issue:
The base class implementation
EditableText#_backspaceScriptHelper for handling the Ctrl+Backspace keyboard shortcut retrieves the text to announce as deleted by expanding the text info to the corresponding text unit and then retrieving the text. This gives an incorrect result in at least Libreoffice Writer, where that would return a string just containing the space character when removing a word followed by a space using the Ctrl+backspace keyboard shortcut.
(Writer's IAccessibleText::textAtOffset implementation that gets used in IA2TextTextInfo#_getWordOffsets handles the space as a separate word, but Ctrl+backspace removes both, the actual word and following whitespace.)
Description of user facing changes
When removing a word followed by whitespace in Libreoffice Writer, the actually removed text is announced.
Description of development approach
Instead of separately retrieving the text for a word, override the default implementation in the LibreOffice app module and announce the actually removed text when handling Ctrl+backspace.
Use the caret position before and after the text has been removed to identify what the removed text is.
