Use coercion for MaskedTextBox.Text

[MrJul]

What does the pull request do?

This PR uses coercion to change MaskedTextBox.Text whenever Text is externally changed to a value that doesn't match the mask.

What is the current behavior?

The Text property is immediately changed back in OnPropertyChanged, causing reentrancy and property change events to be sent out of order. See #16746 (comment) for more context.

What is the updated/expected behavior with this PR?

Extra property change events aren't raised.
The invalid value is invisible to external listeners.

How was the solution implemented?

The new implementation uses a coercion callback.

The coercion callback from TextBox has been exposed as a virtual CoerceText method, since it's responsible for undo/redo. Without this, using OverrideMetadata(TextProperty) on any TextBox descendant breaks the undo/redo feature.

Checklist

• Added unit tests (if possible)?
• Added XML documentation to any related classes?

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0052182-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[maxkatz6]

Technically a new API, as this method wasn't protected previously.
But LGTM.