RFR: 8267565: Support "@3x" and greater high-density image naming convention

[Kevin Rushforth]

On Fri, 22 Mar 2024 16:17:29 GMT, drmarmac <duke at openjdk.org> wrote:

> This PR extends the range of hi-res images that are loaded via naming convention, now including scale factors higher than `@2x`. 
> Supporting these is already being [recommended](https://developer.apple.com/design/human-interface-guidelines/images#Best-practices) for some platforms.
> 
> I tested this manually on Windows with "300%" UI scale factor, and verified `@2x` still works on macOS.

The code changes and test changes look good to me.

@drmarmac Please enable running GitHub Actions in your personal fork of the jfx repo, and trigger a test run so we can see the results (the bot will make them available in this PR once it runs to completion).

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PR Comment: https://git.openjdk.org/jfx/pull/1429#issuecomment-2021332454