8359862: RichTextArea: prompt

[andy-goryachev-oracle]

Adds the prompt attribute to the RichTextArea, to be shown when the model is null or empty.

To allow for greater flexibility, the type of this property is Object, and there is an additional setter that accepts Supplier<Object>. The value of the property, or the value provided by the Supplier<Object> is interpreted as follows:

• null: the prompt is disabled
• Node: the node to be shown
• String: the text will be shown inside a Label with style .prompt
• Object: the toString() value will be shown similarly to the String value

The main idea is to have only one property and allow complex graphics to be shown.

Example:

        setPrompt("a");
        setPrompt(this::getPrompt);
        setPrompt(() -> new Object());
        setPrompt(new Object());
        setPrompt(null);
        setPrompt((String)null);
        setPrompt((Supplier)null);

/csr

---

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---

Progress

• Change must not contain extraneous whitespace
• Change requires CSR request JDK-8389649 to be approved
• Commit message must refer to an issue
• Change must be properly reviewed (2 reviews required, with at least 1 Reviewer, 1 Author)

Issues

• JDK-8359862: RichTextArea: prompt (Enhancement - P4)
• JDK-8389649: RichTextArea: prompt (CSR)

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[bridgekeeper]

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Webrevs

• 01: Full - Incremental (7bf17091)
• 00: Full (67e99d8c)

[andy-goryachev-oracle]

@azuev-java @kevinrushforth could you review this PR please?