* Add markdown code templates and way to specify to use them

- add new preference constant CODEGEN_USE_MARKDOWN
- add new markdown comment templates to default-templates.properties
- add new Markdown Comments category to the CodeTemplateBlock class
  which displays the new markdown comment templates
- add new CodeGenerationContextTypes for new templates
- modify StubUtility methods that create comments to use the new
  templates if markdown should be used (new option on and JVM 23+)
- add new GenerateGettersSettersTest23 to show new behavior
- add new tests to JavadocQuickFixTest25 where new comments get
  added to show they honor the new preference
- fixes #2554