Adopt new tree in Problems panel

[joaomoreno]

• Extract CodeActions related code out of the model
• Remove filtering from the model
• Slim down model to its essence
• Replace tree with ObjectTree
• Add filtering back
• Implement collapse all
• Add context menus back
• Cleanup console.warn calls
• Type in tree and focus the input field

cc @sandy081 will ask you for review later in the milestone 👍

[joaomoreno]

Got mouse and keyboard navigation working in a very dirty way after 2 days. Now just found out that context menu actions are globally registered commands and everything works through context key service... this is a nightmare.

[joaomoreno]

OK easier than expected, getting closer.

[joaomoreno]

@sandy081 This is READY for a good smoketest by you and to be merged to master. There WILL be bugs. 🐛

The only missing piece is the accessibility provider, which the list doesn't yet support, but should be easy to get in.

[joaomoreno]

Bug:

1. reload workbench with text in the filter box, filtering every single result out
2. type more text into the filter box
3. clear filter

tree doesn't appear!

[sandy081]

Good Job @joaomoreno