RFR: 8378578: Add final to XbmColormap and XbmHints in XbmImageDecoder

[Damon Nguyen]

On Tue, 24 Feb 2026 15:50:57 GMT, Alexey Ivanov <aivanov at openjdk.org> wrote:

> A trivial clean up for `XbmImageDecoder` that marks the fields `XbmColormap` and `XbmHints` with the `final` modifier. These fields are constants.
> 
> In addition to the above, improve the javadoc by using the `@snippet`. Otherwise, all the lines of the XBM snippet are combined into one line.

Marked as reviewed by dnguyen (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/29896#pullrequestreview-3850563072