Migrate LoggerFields to use typed parameters in factory method.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1597380 13f79535-47bb-0310-9956-ffa450edef68
Use Assert.requireNonNull.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1597383 13f79535-47bb-0310-9956-ffa450edef68
Remove unused constructor from PluginManager.

  - The expected class field isn't used anywhere in PM, so it doesn't make sense to include it as a field.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1597385 13f79535-47bb-0310-9956-ffa450edef68
Make PluginBuilder returned a typed plugin instead of Object.

  - It would make perfect sense to assume that the class used in the constructor works as the type to return from the factory method.
  - Even when we add plugin builder classes, that shouldn't affect the PluginType<T> parameter.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1597386 13f79535-47bb-0310-9956-ffa450edef68
Migrate HtmlLayout to use typed parameters in factory method.

  - Also added createDefaultLayout method for convenience.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1597387 13f79535-47bb-0310-9956-ffa450edef68
Make instance field private.

  - Really now, there's no good reason to make a field protected AND final.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1597388 13f79535-47bb-0310-9956-ffa450edef68
Update XmlLayout to use typed parameters in factory method.

  - Also added createDefaultLayout method for convenience.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1597389 13f79535-47bb-0310-9956-ffa450edef68