Add XML docs for Action-based Java.Lang.Thread constructors

[Copilot]

The Java.Lang.Thread convenience constructors that accept Action were public API surface without XML docs, which left IntelliSense/API docs incomplete. This update adds constructor-level documentation for all five Action-based overloads in Thread.cs.

• API docs: Action-based Thread overloads

  • Added /// <summary> to each Action-based constructor.
  • Added /// <param> entries for runHandler, threadName, group, and stackSize where applicable.
  • Added Android reference links via /// <seealso href="..."> using existing Mono.Android documentation style.

• Scope

  • Documentation-only change in src/Mono.Android/Java.Lang/Thread.cs.
  • No behavioral or signature changes.

/// <summary>
/// Initializes a new <see cref="Thread"/> with the specified name that runs the specified <paramref name="runHandler"/> when started.
/// </summary>
/// <param name="runHandler">The delegate to execute on the new thread.</param>
/// <param name="threadName">The name of the new thread.</param>
/// <seealso href="https://developer.android.com/reference/java/lang/Thread#Thread(java.lang.Runnable,%20java.lang.String)">Android documentation for <c>java.lang.Thread</c></seealso>
public Thread (Action runHandler, string threadName) : this (new RunnableImplementor (runHandler), threadName) {}

• Fixes [fix-finder] Add XML documentation to Action-based Java.Lang.Thread constructors #12264