tdf#149255 qt: Implement deletion/"swallowing" for IM replacement

This implements deletion of the text specified by the
`replacementStart()` and `replacementLength()` of the
`QInputMethodEvent*` received in `QtWidget::inputMethodEvent`.

Quoting from the `QInputMethodEvent` doc [1]:

> When receiving an input method event, the text widget has to performs
> the following steps:
>
> 1. If the widget has selected text, the selected text should
>    get removed.
> 2. Remove the text starting at replacementStart() with length
>    replacementLength() and replace it by the commitString().
> [...]

This implementation is sufficient for the scenario described in tdf#149255,
but I didn't test any more complex scenarios, like one where text is selected.
(My current knowledge of input methods is too limited to be able to do
more extensive testing without first spending time to get deeper into
the topic.)

The gtk3 implementation in
`GtkSalFrame::IMHandler::signalIMDeleteSurrounding`
was very helpful to get an impression of what needs to be done.

Since the documentation for `QInputMethodEvent::replacementLength()`
talks about "number of characters", I suspect that conversion
to UTF-16 code units is needed just the same way as it is for the
gtk3 case and this therefore calls
`SalFrame::CalcDeleteSurroundingSelection` the same way.
However, this part is untested, since it is not relevant
for the tested scenario (where each of the characters is represented
in a single UTF-16 code unit).

[1] https://doc.qt.io/qt-5/qinputmethodevent.html

Change-Id: I2a34e58067e253c39dbd87905943134bdfa4ea27
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/134855
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>

0 files changed, 0 insertions, 0 deletions