Add default and customizable ARIA semantics to DataGrid select column

[Codex]

DataGrid row selection lacked default ARIA labels and did not expose selection state via aria-selected, blocking accessible defaults and customization.

• Default ARIA labels: Select checkboxes now emit localized labels (“Select row {index}”, “Select all rows”) via new language resources.
• Customizable labels: SelectColumn accepts RowCheckboxAriaLabelFunc, RowCheckboxAriaLabelledByFunc, SelectAllAriaLabel, and SelectAllAriaLabelledBy to override defaults per row/header.
• Selection semantics: Data rows render aria-selected reflecting current selection; row index flows through CellContext to support label generation.
• Tests: Added unit coverage for default/custom labels and aria-selected updates.

Example:

<MudDataGrid Items="people" MultiSelection>
  <Columns>
    <SelectColumn T="Person"
                  RowCheckboxAriaLabelFunc="(item, i) => $"{item.Name} row {i + 1}""
                  SelectAllAriaLabel="Select everyone" />
    <PropertyColumn T="Person" Property="p => p.Name" />
  </Columns>
</MudDataGrid>

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Add default and customizable ARIA labeling and selection semantics to DataGrid SelectColumn</issue_title>
<issue_description>## Objective
Implement default and customizable ARIA accessibility behavior for MudDataGrid row selection checkboxes, aligned with accessibility corrections introduced in follow-up PR 125914.

This change applies only to:

• aria-label
• aria-labelledby
• aria-selected

Do not implement aria-controls.

---

Scope & Context

• SelectColumn.razor and SelectColumn.razor.cs control the MudCheckBox instances used for row selection in MudDataGrid.
• The DataGrid owns selection state and must expose correct ARIA semantics by default.
• The solution must be non-breaking and require no user configuration for standard scenarios.

---

Functional Requirements

1. Default ARIA labeling (no user configuration)

• Provide default ARIA labels for selection checkboxes when no customization is supplied.
• Must apply to:
  • Per-row selection checkboxes
  • Header “select all” checkbox

Default behavior:

• Use aria-label by default.
• Labels must be deterministic and screen-reader friendly.

Example expectations (illustrative):

• Row checkbox: "Select row" or "Select row {index}"
• Header checkbox: "Select all rows"

Do not require developers to explicitly enable this behavior.

---

2. Customizable ARIA labeling

• SelectColumn must expose a way to customize ARIA labels for row selection checkboxes.
• Customization must:
  • Be optional
  • Be context-aware (row data available)
  • Override default ARIA labels when provided

Acceptable mechanisms include (implementation choice left open):

• Delegate (e.g., Func<TItem, string>)
• Context-aware provider or template
• Parameter allowing override of default ARIA attributes

If customization is supplied:

• It must replace the default aria-label
• It must not remove ARIA labeling entirely unless explicitly intended

---

3. aria-selected behavior (default and automatic)

• Selected rows must correctly expose aria-selected="true" or "false".
• This must reflect the actual DataGrid selection state at all times.
• This behavior must be automatic and enabled by default.

Guidance:

• aria-selected is applied to the row (or row-equivalent element).
• MudCheckBox may participate in state propagation, but the DataGrid owns correctness.

No configuration should be required to enable aria-selected.

---

4. Explicit Non-Goals

• Do not implement aria-controls.
• Do not introduce breaking API changes.
• Do not require consumers to manually wire ARIA attributes for standard DataGrid selection scenarios.

---

Unit Tests

Add or update unit tests to validate the following:

1. Default labeling

• Row selection checkboxes render with a non-empty aria-label when no customization is provided.
• Header “select all” checkbox renders with a non-empty aria-label.

2. Custom labeling

• When a custom ARIA label provider is supplied:
  • The rendered checkbox uses the custom label.
  • The default label is not rendered.
• Custom labels receive correct row context.

3. aria-selected state

• Selecting a row sets aria-selected="true" on the corresponding row element.
• Deselecting a row sets aria-selected="false".
• Header “select all” correctly updates aria-selected on all rows.

4. Regression safety

• Existing DataGrid selection behavior remains unchanged.
• No exceptions or warnings occur when no ARIA customization is provided.

Tests should be written using existing MudBlazor test patterns and utilities.

---

Acceptance Criteria

• Selection checkboxes are screen-reader accessible by default.
• Developers can customize ARIA labels without re-templating the SelectColumn.
• aria-selected accurately reflects row selection state.
• Behavior aligns with ARIA grid / table selection best practices.
• All new behavior is covered by unit tests.

---

Notes for Implementation

• Keep logic centralized in SelectColumn / DataGrid infrastructure.
• Prefer defaults over configuration.
• Treat accessibility behavior as part of the public contract.
  </issue_description>

Comments on the Issue (you are @codex[agent] in this section)

• Fixes Add default and customizable ARIA labeling and selection semantics to DataGrid SelectColumn #3

[versile2]

Superseded by MudBlazor#12911 after rebasing onto current upstream/dev and splitting the follow-up fixes into separate commits.