Implement dispose pattern for InputFile

[Copilot]

Implement dispose pattern for InputFile

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Implement standard .NET dispose pattern in InputFile

Description

InputFile previously used explicit interface implementation for IDisposable.Dispose(), making it difficult for derived classes to properly dispose resources without reflection. Now implements the standard dispose pattern with a protected virtual method.

Changes:

• Add protected virtual void Dispose(bool disposing) method containing disposal logic
• Update IDisposable.Dispose() to call Dispose(true)
• Add unit test verifying derived classes can override disposal behavior
• Update public API surface

Pattern follows:

protected virtual void Dispose(bool disposing)
{
    if (disposing)
    {
        _jsCallbacksRelay?.Dispose();
    }
}

void IDisposable.Dispose()
{
    Dispose(disposing: true);
}

Derived classes can now override Dispose(bool) without reflection, consistent with InputBase and ValidationMessage.

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Blazor] InputFile should implement dispose pattern</issue_title>
<issue_description>I implemented a derived class of InputFile for handling the cancel event (see also #58118).
I had to use reflection to dispose _jsCallbacksRelay. InputFile should implement the dispose pattern to make it easier for derived classes to properly dispose of resources.</issue_description>

<agent_instructions>Use the Microsoft docs to learn how to properly implement the Dispose pattern inside InputFile and do so.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes [Blazor] InputFile should implement dispose pattern #64392

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