Fix documentation: Replace non-existent ISerializer.Serialize method with ToString

[Copilot]

The serialization documentation incorrectly referenced a Serialize method that doesn't exist on the ISerializer interface. This was causing confusion for developers trying to follow the documentation examples.

Problem:
The documentation showed this example:

public void Serialize()
{
    var myObject = new Person();
    var json = _serializer.Serialize(myObject);  // ❌ Method doesn't exist
}

Solution:
The ISerializer interface provides a ToString(object value, Type valueType) method, with a generic extension method ToString<T>(T value) available. The correct usage is:

public void Serialize()
{
    var myObject = new Person();
    var json = _serializer.ToString(myObject);  // ✅ Uses extension method
}

This fix aligns the documentation with:

• The actual ISerializer API implementation
• Other examples in the documentation that correctly use ToString
• The patterns used in the test suite
• The extension methods provided in SerializerExtensions

Fixes #2852.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• uno-assets.platform.uno
  • Triggering command: dotnet build src/Uno.Extensions.Serialization/Uno.Extensions.Serialization.csproj (dns block)
  • Triggering command: dotnet build src/Uno.Extensions.Serialization/Uno.Extensions.Serialization.csproj --verbosity quiet (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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[kazo0]

@copilot you need to adjust the commits to conform to Conventional Commits as defined by https://www.conventionalcommits.org/en/v1.0.0/

[Copilot]

@copilot you need to adjust the commits to conform to Conventional Commits as defined by https://www.conventionalcommits.org/en/v1.0.0/

I've updated the commit to follow Conventional Commits format. The commit message now uses:

• docs: type prefix for documentation changes
• Lowercase descriptive summary without trailing period
• Detailed body explaining the problem and solution
• Footer with Fixes #2852 reference

The commits have been restructured to remove the unnecessary "Initial plan" commit and have a single focused commit with proper formatting per the specification.