Add 26.1 WPF docs for RangeBarSeries across chart, changelog, and what's new topics

[Copilot]

This updates the WPF bar chart documentation for the new RangeBarSeries introduced in 26.1. It adds the feature to the main release surfaces and mirrors the relevant content in Japanese.

• New chart topic

  • Added dedicated English and Japanese topics for RangeBarSeries
  • Documented:
    • series purpose and orientation vs. RangeColumnSeries
    • required axes (NumericXAxis + CategoryYAxis)
    • core member paths and legend-related properties
    • a minimal XAML example

• Release documentation

  • Added new 2026 Volume 1 what's new topics in English and Japanese
  • Linked the new 2026 Volume 1 topics from the existing what's new index pages
  • Added 26.1 changelog entries in English and Japanese calling out RangeBarSeries

• Related chart references

  • Updated the xamDataChart styling/reference topics to include RangeBarSeries alongside the other supported series types

• Docs consistency

  • Kept topic naming/linking aligned with existing datachart-* conventions
  • Corrected the nearby changelog TOC anchor for 25.2.107 while touching that section

<ig:XamDataChart>
    <ig:XamDataChart.Axes>
        <ig:NumericXAxis x:Name="xAxis" />
        <ig:CategoryYAxis x:Name="yAxis"
                          ItemsSource="{Binding}"
                          Label="{}{Label}" />
    </ig:XamDataChart.Axes>
    <ig:XamDataChart.Series>
        <ig:RangeBarSeries ItemsSource="{Binding}"
                           LowMemberPath="Low"
                           HighMemberPath="High"
                           XAxis="{Binding ElementName=xAxis}"
                           YAxis="{Binding ElementName=yAxis}" />
    </ig:XamDataChart.Series>
</ig:XamDataChart>

[IGvaleries]

same comment as other PRS that we haven't been using whats-new topics anymore and have just been using the changelog