The GenerateMarkerKey method in SSRRenderModeBoundary was failing when string values were passed as component keys because strings don't implement IFormattable. This caused string keys to be converted to empty strings instead of preserving their actual values.

Problem

The original code attempted to cast all component keys to IFormattable:

var formattedComponentKey = (componentKey as IFormattable)?.ToString(null, CultureInfo.InvariantCulture) ?? string.Empty;

When a string was passed as the key, the cast to IFormattable would fail (since string doesn't implement IFormattable), resulting in an empty string instead of the actual string value.

Solution

Updated the method to use pattern matching with explicit handling for strings:

var formattedComponentKey = componentKey switch
{
    string str => str,
    IFormattable formattable => formattable.ToString(null, CultureInfo.InvariantCulture),
    _ => string.Empty
};

This ensures that:

• String keys are used directly without formatting
• IFormattable types (int, Guid, DateTime, etc.) are properly formatted using InvariantCulture
• Non-formattable objects default to empty string

Tests Added

Added comprehensive tests for all common primitive types:

• String keys (the main fix)
• Integer keys
• Guid keys
• Double keys
• DateTime keys
• Null keys
• Non-formattable object keys

All tests verify that the keys are properly formatted and preserved in the ComponentMarkerKey.FormattedComponentKey property.

Fixes #62813.

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