Make it possible to disable legacy Property.toString and related warning message

[vaadin-bot]

Originally by @Artur-

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The toString() method in AbstractField and Label logs an error message and returns the property value in 7.0. The log message promises neither will happen in 7.1 anymore.

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Imported from https://dev.vaadin.com/ issue #10916

[vaadin-bot]

Originally by @Artur-

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Review meeting decided this has the potential to break too much and should be reverted.

[vaadin-bot]

Originally by @Artur-

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Review meeting decided this has the potential to break too much and should be reverted.

[vaadin-bot]

Originally by @Artur-

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Decided to keep the current behavior for now to avoid breaking legacy code but to add a way to disable the feature and related log message.

[vaadin-bot]

Originally by @Artur-

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Decided to keep the current behavior for now to avoid breaking legacy code but to add a way to disable the feature and related log message.

[vaadin-bot]

Originally by @Artur-

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The init parameter "legacyPropertyToString" now controls the behavior of Property.toString for old Property implementations. A value of "true" or "warning" enables the legacy behavior, "false" disables it. If set to "warning" (the default) then a warning will be emitted when toString is called (like in 7.0).

[vaadin-bot]

Originally by @Artur-

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The init parameter "legacyPropertyToString" now controls the behavior of Property.toString for old Property implementations. A value of "true" or "warning" enables the legacy behavior, "false" disables it. If set to "warning" (the default) then a warning will be emitted when toString is called (like in 7.0).