Extend ColorEditor to include alpha channel

### Description

The `org.netbeans.beaninfo.editors.ColorEditor` class does not support the alpha channel. This `PropertyEditor` is used in various places.

The color chooser UI allows to set the transparency but then it's ignored.

Do I miss something or it's a gap?

You can reproduce it by
1. Create a new JPanel and change the background color
2. Select a color with transparency
3. Close the editor and reopen it, the transparency setting is gone

### Use case/motivation

In some cases one want to select a color with the alpha channel. As a default color editor, it should support it.

### Related issues

_No response_

### Are you willing to submit a pull request?

Yes

### Code of Conduct

Yes

Start with org.netbeans.beaninfo.editors.ColorEditor and reproduce the JPanel background-color workflow described in the issue. Trace how the color chooser stores and restores transparency; done means selecting a color with an alpha channel and reopening the editor preserves that setting.

Written by the indexing model from the issue text.