Implement input method support to COSMIC specific text widgets

[kenz-gelsoft]

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This is a FYI PR for future reference after the COSMIC team rebased the libcosmic to iced 14.0.

The input method support in iced 14.0 requires text widgets to implement some logic to support input method input. This PR includes this for the COSMIC specific text widgets.

This PR depends on my pop-os/iced fork. Please see PRs I opened:

• Backport the input method support only from iced 0.14 iced#255
• Support ime on sctk windows iced#256

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Changes in this PR

Opt-in the IME feature of the toolkit when text widgets have focus

• specifies the position of the IME candidates window from the caret location or the selection region.

Handles optional IME events in text widgets

• to show the composing text (a.k.a. preedit) by passing through it to the toolkit.
• to commit the composing text by reusing the clipboard paste logic.

(I will force-push this branch to update my fork to rebase to newer upstream rev)