Update docs for TreeDataGrid 12.

[grokys]

Quite a lot has changed in TreeDataGrid 12, so the docs needed a fair bit of a rework.

From the release notes:

• Define TreeDataGrid columns from XAML
• Major refactoring of API - see breaking changes doc
• Fluent columns API
• Unified SelectionChangedEventArgs for row and cell selection
• Experimental bindings removed - TreeDataGrid now uses standard Avalonia bindings

[Copilot]

Pull request overview

Updates the TreeDataGrid documentation set to reflect the TreeDataGrid v12 API refactor and the new recommended workflows (XAML-defined columns and fluent code-behind column creation), and adds a dedicated v12 migration/breaking-changes page.

Changes:

• Reworks TreeDataGrid docs to use the v12-style XAML column definitions and fluent column builder APIs.
• Adds/updates guidance for selection, sorting, filtering, and expand/collapse behavior under the v12 model.
• Introduces a new “TreeDataGrid v12 breaking changes” document and links it from navigation.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
controls/data-display/structured-data/treedatagrid/sorting.md	Updates sorting guidance/examples for v12 patterns (XAML columns + fluent options).
controls/data-display/structured-data/treedatagrid/selection-modes.md	Adds XAML selection mode guidance and updates selection event docs for v12.
controls/data-display/structured-data/treedatagrid/index.md	Restructures overview/quickstart for v12 workflows; adds upgrade tip and updated install guidance.
controls/data-display/structured-data/treedatagrid/filtering.md	Clarifies filtering constraints and updates examples to fluent column setup.
controls/data-display/structured-data/treedatagrid/expand-and-collapse.md	Updates hierarchical expand/collapse examples to fluent APIs and new event arg usage.
controls/data-display/structured-data/treedatagrid/column-types.md	Rewrites column types page for new column types, XAML usage, and fluent code-behind APIs.
controls/data-display/structured-data/treedatagrid/breaking-changes-v12.md	Adds a v12 migration guide documenting breaking API changes.
controls-sidebar.ts	Adds the new breaking-changes page to the TreeDataGrid docs sidebar.

Comments suppressed due to low confidence (1)

controls/data-display/structured-data/treedatagrid/index.md:113

• The sample data includes an extra trailing space in the FirstName string literal ("Lailah "). This can lead to confusing output/sorting/filtering results in examples; remove the trailing space.

        new Person { FirstName = "Jeremy", LastName = "Navarro", Age = 74 },
        new Person { FirstName = "Lailah ", LastName = "Velazquez", Age = 16 },
        new Person { FirstName = "Jazmine", LastName = "Schroeder", Age = 52 },

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[Copilot]

This page introduces an ItemsSource property and a XAML-first workflow. However, the generated API reference currently in this repo for Avalonia version-12.0.0-preview2 documents TreeDataGrid as having Source/Columns but no ItemsSource (see api_versioned_docs/version-12.0.0-preview2/avalonia/controls/treedatagrid.mdx). To avoid readers hitting a mismatch between the conceptual docs and the API reference, consider version-gating these docs, adding a note about the required TreeDataGrid package build, or coordinating the API reference update.

[grokys]

We'll need to update the API reference when the package is pushed.

[Copilot]

This section states that key TreeDataGrid interfaces (e.g. ITreeDataGridSource, IColumn) were replaced with abstract classes. However, the generated API reference currently present in this repo for version-12.0.0-preview2 still documents these as interfaces (e.g. api_versioned_docs/version-12.0.0-preview2/avalonia/controls/itreedatagridsource.mdx and .../models/treedatagrid/icolumn.mdx). To avoid confusing readers, either update/coordinate the API reference, or clarify in this doc which TreeDataGrid package version/preview the change applies to (and whether the interfaces remain as obsolete shims).

[grokys]

We'll need to update the API reference when the package is pushed.

[luke-whos-here]

Left a few comments and suggestions.

Overall, the new docs are clear, user-friendly and consistent when similar topics are addressed between different pages. Additional cross-links to relevant pages could be nice, but not strictly necessary.

[luke-whos-here]

Left a few comments and suggestions.

Overall, the new docs are clear, user-friendly and consistent when similar topics are addressed between different pages. Additional cross-links to relevant pages could be nice, but not strictly necessary.