Feature: auto collapse all chunks on load

[ViscousPot]

Describe the feature
It would be great to have a flag on the code_editor or controller that auto collapses all the chunks in a file before loading.

Why it's worth it
I was initially just looking to do this for convenience when looking at a particular file that is in an expected format, while using a custom ChunkAnalyzer. Basically to just hide the unimportant bits in a log file. But after implementing it, and then replacing the editor with a loading spinner while collapsing the chunks, the highlight analysis actually happened a lot faster.

I have to assume what happened was that the highlight analysis was held off until after everything was collapsed so it had less to analyse. So, could be helpful against this (#2), to reduce the initial load.

The code I'm using to collapse all the chunks (doubt it's the best way)

WidgetsBinding.instance.addPostFrameCallback((_) async {
  if (controller.text.isEmpty) return;
  chunksCollapsed = false;

  var chunkController = ReEditor.CodeChunkController(controller, LogsChunkAnalyzer());
  while (chunkController.value.isEmpty) {
    await Future.delayed(Duration(milliseconds: 100));
  }
  int offset = 0;

  for (final chunk in chunkController.value) {
    chunkController.collapse(chunk.index - offset);
    offset += max(0, chunk.end - chunk.index - 1);
  }
  
  chunksCollapsed = true;
  setState(() {});
});

and then in the UI

!chunksCollapsed
  ? Center(child: CircularProgressIndicator(color: Colors.white))
  : CodeEditor( ...