maintenance: improve performance of decorating documents and add an option to disable the reference provider

[tintinweb]

• adds an option to disable the reference provider
• only decorates when needed
  • before this change we decorated the editor multiple times (once when initially analyzing the file concurrent to resolving symbols and the outline). the new behavior is that we only decorate when we know which editor window triggered the analysis (symbols/outline don't). One drawback of this is that at least for startup (or opening a new file) we have to rely on the current active editor. hence, there is still a slight chance of decorations being applied to the wrong window if quickly switching between editors.
• refactored uml export (+drawio)