LocalPlantUmlRenderer is not works on non-Windows environment

[filzrev]

On Ubuntu environment.

PlantUml.Net failed to resolve Java executable path.
It occurred when running PlantUml.Net with RenderingMode = RenderingMode.Local.

It's seems to be caused because EnvironmentJavaLocator::GetJavaInstallationPath methods assuming executable name as java.exe.
(On non-Windows environment. It need to specify without .exe extension)

Additionally, when specifying java executable path with JavaPath settings explicitly.
Process hanged at LocalPlantUmlRenderer::RenderAsync method on Ubuntu OS.

Code to reproduce problems

internal class Program
{
    static async Task Main(string[] args)
    {
        var factory = new RendererFactory();

        var renderer = factory.CreateRenderer(new PlantUmlSettings
        {
            JavaPath = "/usr/bin/java",
            ErrorReportMode = ErrorReportMode.Verbose,
            RenderingMode = RenderingMode.Local,
        });

        var bytes = await renderer.RenderAsync("Bob -> Alice : Hello", OutputFormat.Png);
        File.WriteAllBytes("out.png", bytes);
    }
}

See: dotnet/docfx#10435