Summary
Removes allowUndo parameter from RichTextArea::replaceText.
Adds a boolean undoRedoEnabled attribute to the StyledTextModel.
Note that this is NOT a backward-compatible change, as a part of the incubator iteration.
Problem
Early user feedback asked for addition of allowUndo parameter to applyStyle() and setStyle() methods in the  StyledTextModel, to mirror the parameter in replaceText().
However, selectively enabling or disabling the undo functionality corrupts the internal state. Instead, to address use cases that require disabled undo, such as programmatically building the document content, a single boolean flag is added to the model. Disabling undo also clears the undo/redo stack.
Solution
The solution is to remove the offending parameter and add a flag.
Additionally, similar methods are added to the RichTextArea class that forward the calls to the model (or do nothing if the model is null).
Specification
See the attached diffs.
- csr of
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JDK-8366201 RichTextArea: remove allowUndo parameter
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     - In Progress
 
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