RFR: JDK-8307807 Replace use of System.getProperty("os.name") with PlatformUtil calls

[Carl Döbbelin]

On Wed, 10 May 2023 18:47:16 GMT, Carl Döbbelin <duke at openjdk.org> wrote:

> Replaced querying of `System.getProperty("os.name")` to check for OS with the use of the methods provided by `PlatformUtils`

I cannot use the PlatformUtils in the `com.sun.webkit.network.URLLoader` class, as the PlatformUtils are not Exported to the corresponding module.

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PR Comment: https://git.openjdk.org/jfx/pull/1132#issuecomment-1544146865