Implement nested Label for DisplayName

[ilonatommy]

Add Label component for Blazor Forms

Add Label component that renders accessible labels using wrapping pattern

Description

This PR adds a new Label<TValue> component that renders an HTML <label> element with the display name extracted from [Display] or [DisplayName] attributes, falling back to the property name.

Details in #64791 (comment)

Usage

<Label For="() => model.Name">
    <InputText @bind-Value="model.Name" />
</Label>

Renders:

<label>
    Name
    <input name="model.Name" ... />
</label>

Design

Uses the wrapping pattern where the input is nested inside the label, providing implicit HTML label-input association without requiring for/id attribute matching. This approach:

• Requires no changes to existing InputBase or Input* components
• Has no breaking changes
• Supports AdditionalAttributes for styling (e.g., class="form-label")
• Supports ChildContent for nesting input components

Fixes #64791

[Copilot]

Pull request overview

This PR implements a new Label<TValue> component for Blazor Forms that renders an HTML <label> element with display name extraction from [Display] or [DisplayName] attributes. The component uses a wrapping pattern where input components are nested inside the label element, providing implicit HTML label-input association without requiring for/id attribute matching.

Key Changes

• Added Label<TValue> component that implements IComponent for rendering accessible form labels
• Component extracts display names using the existing ExpressionMemberAccessor.GetDisplayName utility
• Comprehensive unit test suite covering various scenarios including attribute precedence, nested properties, and child content rendering

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/Components/Web/src/Forms/Label.cs	Implements the new Label<TValue> component with parameter handling, display name extraction, and render tree building
src/Components/Web/test/Forms/LabelTest.cs	Adds comprehensive unit tests covering display name extraction, attributes, child content, and error scenarios
src/Components/Web/src/PublicAPI.Unshipped.txt	Documents the new public API surface for Label<TValue> component

[maraf]

What happens if user adds for attribute manually?