UI locks up on running rust-analyzer

[hsnoil]

Bug Description:

When using rust-analyzer(with proper binary) on the appimage, I ran into UI locking up issues on certain code after saving the first time.

I have no issues running this in vscode, but in theia it locks up the HTML UI.

The native UI still works but does not accept commands and I have to kill the theia process

Steps to Reproduce:

1. Use Theia appimage
2. Install rust-analyzer plugin (insure you are using proper binary)
3. Extract the minimum example code: test1.zip
4. Go to main.rs and then save, once first save is done. Type let and Theia will freeze up before finishing typing with the suggestions menu open

Additional Information

• Operating System: Linux
• Theia Version: 1.50.100

[msujew]

Took a quick look at this. It seems like our problem tree widget runs into an infinite loop here:

theia/packages/core/src/browser/tree/tree-widget.tsx

Lines 334 to 337 in 49b8735

	for (const node of new TopDownTreeIterator(root, {
	pruneCollapsed: true,
	pruneSiblings: true
	})) {

Which then eventually yields a out of memory error. Taking a look at the tree model shows a cyclic reference between tree nodes (which makes them non-tree nodes from a graph perspective). I'll take a further look at this later and see what the root cause is. It's likely based on how we update/modify the problem tree model.

[msujew]

See #13841 for a fix.