.NET 10 P5 - WPF (#9918)

* wpf

* Add notes

---------

Co-authored-by: Andy (Steve) De George <[email protected]>

Author: jamesmontemagno

release-notes/10.0/preview/preview5/wpf.md

@@ -2,12 +2,44 @@
 
 Here's a summary of what's new in WPF in this preview release:
 
-- [Feature](#feature)
+- [XAML Grid Syntax Enhancements](#xaml-grid-syntax-enhancements)
+- [Font and Globalization Updates](#font-and-globalization-updates)
+- [Fluent Theme Improvements](#fluent-theme-improvements)
+- [Performance and Code Quality Improvements](#performance-and-code-quality-improvements)
 
 WPF updates in .NET 10:
 
 - [What's new in WPF in .NET 10](https://learn.microsoft.com/dotnet/desktop/wpf/whats-new/net100) documentation.
 
-## Feature
+## XAML Grid Syntax Enhancements
 
-Something about the feature
+This release introduces a new shorthand syntax for defining `Grid.RowDefinitions` and `Grid.ColumnDefinitions` in XAML, with full support for XAML Hot Reload.
+
+**Example:**
+
+```xml
+<Grid RowDefinitions="Auto,*,Auto" ColumnDefinitions="*, Auto">
+    <TextBlock Text="Row 0, Col 0" Grid.Row="0" Grid.Column="0" />
+    <TextBlock Text="Row 1, Col 1" Grid.Row="1" Grid.Column="1" />
+    <TextBlock Text="Row 2, Col 0" Grid.Row="2" Grid.Column="0" />
+</Grid>
+```
+
+This shorthand allows you to specify row and column sizes directly in the `RowDefinitions` and `ColumnDefinitions` attributes, making XAML more concise and readable.
+
+## Font and Globalization Updates
+
+The `simsun-extg` font has been added to improve character rendering, especially for East Asian languages.
+
+## Fluent Theme Improvements
+
+Resolved crashes in the Fluent theme related to the `TextBox` control. Enhanced styling for `SelectionBrush` and `Thumb` controls, and improved visual accuracy by correcting the `Expander` arrow direction in right-to-left (RTL) layouts.
+
+## Performance and Code Quality Improvements
+
+This release includes several improvements to performance and code quality:
+
+- Reduced memory allocations by replacing boxed collections such as `ArrayList`, `Hashtable`, and `IList` with more efficient alternatives like arrays and generic collections.
+- Optimized internal logic by refining parsing routines and removing unused fields in utilities such as `DpiHelper` and `XamlSchema`.
+- Eliminated the static constructor from `KnownColors` to improve runtime performance.
+- Removed legacy or unused code, including the `ReflectionHelper` for WinRT.