Check element readiness based on the "$" property not just the "root" property

[denis-anisimov]

Fix for #3277

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This change is 

[vaadin-bot]

SonarQube analysis reported 2 issues

Note: The following issues were found on lines that were not modified in the pull request. Because these issues can't be reported as line comments, they are summarized here:

1. SimpleElementBindingStrategy.java#: This file has 776 lines, which is greater than 750 authorized. Split it into smaller files.
2. SimpleElementBindingStrategy.java#L690: Refactor this method to reduce its Cognitive Complexity from 17 to the 15 allowed.

[ZheSun88]

Reviewed 6 of 6 files at r1.
Review status: all files reviewed at latest revision, 1 unresolved discussion.

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flow-client/src/test-gwt/java/com/vaadin/client/flow/GwtBasicElementBinderTest.java, line 1206 at r1 (raw file):

        Element shadowRoot = Browser.getDocument().createElement("div");

        WidgetUtil.setJsProperty(element, "root", shadowRoot);

what is the purpose by changing these two lines?
That is not a blocker.

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Comments from Reviewable

[denis-anisimov]

Review status: all files reviewed at latest revision, 1 unresolved discussion, all commit checks successful.

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flow-client/src/test-gwt/java/com/vaadin/client/flow/GwtBasicElementBinderTest.java, line 1206 at r1 (raw file):

Previously, ZheSun88 (Sun Zhe) wrote…

what is the purpose by changing these two lines?
That is not a blocker.

root property has been checked against null in the main code to execute the logic.
Now another property is checked.
The presence of the root property should not do anything.
That what happens: now the root property is set from the very beginning and then after bind and flush nothing should happen. That's checked.

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Comments from Reviewable