fix regressions related to tasks support

[akosyakov]

What it does

• fix Task schema support stops working #8230: ensure that user tasks model is created before opening it
• fix Task schema support stops working #8230: ensure that schema resource exists before updating it

How to test

• test that you can create user and workspace tasks
• test that tasks.json and launch.json files have schema support

Review checklist

• as an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• as a reviewer, I agree to behave in accordance with the review guidelines

[vince-fugnitto]

The changes work well, I verified that:

• user-level tasks
  • tasks run successfully
  • the schemas work correctly, including hover information and problem markers

• workspace-level tasks
  • tasks run successfully
  • the schemas work correctly, including hover information and problem markers

• launch
  • debug sessions run successfully
  • the schema works correctly, including hover information and problem markers

[RomanNikitenko]

@akosyakov
The changes are meaningful and look good to me, but unfortunately they don't fix #8230 for me :-(

I played with your changes and still can reproduce the issue:

• I had theia and vscode folders in my workspace
• I tried to edit tasks.json file from theia folder, then edit tasks.json file from vscode folder
• it happens not at refreshing page, but within editing tasks.json file
• usually it takes a few minutes to face with the issue
• I can reproduce permanently similar problem for settings.json at refreshing page

Please see a few videos.

tasks.json problem
https://youtu.be/ZsO3H-yN9DM
https://youtu.be/KBLBarHtVL0

settings.json problem:

[akosyakov]

@RomanNikitenko sorry was too fast, i am checking again

[akosyakov]

For settings I think it is not a regressions, but an enhancement to support different kind of settings schema: https://github.com/microsoft/vscode/blob/2277c8e2a3e1cc630a6397301ba54a1dccd8a60d/src/vs/workbench/services/configuration/common/configuration.ts#L12-L17 I will file an issue.

[akosyakov]

An issue to support all setting schemas: #8349