Suspend selection updates in TextBoxTextInputMethodClient until all changes are completed

[emmauss]

What does the pull request do?

Suspend sending selection update events from TextBoxTextInputMethodClient until all selection changes in textbox are completed for an action.

What is the current behavior?

Currently, we update selection when caret position changes by first setting the start and end in 2 properties, i.e. SelectionStart and SelectionEnd. Those 2 updates are sent to the OS as 2 selection updates. Because of that, keyboards that support advance editing will detect it as a selection in progress, and will enable the selection flag on the keyboard.

20240506-1749-19.8416805.mp4

What is the updated/expected behavior with this PR?

When selection or caret changes occur for actions handled by TextBox, the selection updates aren't sent to the input method until the action is completed and selection is done.

How was the solution implemented (if it's not obvious)?

Checklist

• Added unit tests (if possible)?
• Added XML documentation to any related classes?
• Consider submitting a PR to https://github.com/AvaloniaUI/avalonia-docs with user documentation

Breaking changes

Obsoletions / Deprecations

Fixed issues

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0048205-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]