Fix show text document view column

[godlin-gh]

What it does

fix #6800 #6801

How to test

1. clone my test plugin into plugins dir and build plugin

mkdir plugins
cd plugins
git clone https://github.com/godlin-gh/vscode-document-api-test.git
cd vscode-document-api-test
yarn
yarn compile

2. add this to launch.json

    {
      "name": "Launch VS Code ShowDocument API Test",
      "type": "node",
      "request": "launch",
      "args": [
        "${workspaceFolder}/examples/browser/src-gen/backend/main.js",
        "${workspaceFolder}/plugins/vscode-document-api-test/testWorkspace",
        "--port",
        "3030",
        "--hostname",
        "0.0.0.0",
        "--extensionTestsPath=${workspaceFolder}/plugins/vscode-document-api-test/out/test/suite/index",
        "--hosted-plugin-inspect=9339"
      ],
      "env": {
        "THEIA_DEFAULT_PLUGINS": "local-dir:${workspaceFolder}/plugins",
        "THEIA_WEBVIEW_EXTERNAL_ENDPOINT": "${env:THEIA_WEBVIEW_EXTERNAL_ENDPOINT}"
      },
      "stopOnEntry": false,
      "sourceMaps": true,
      "outFiles": [
        "${workspaceFolder}/../.js"
      ]
    }

3. debug or run
   
4. open http://localhost:3030
   

There should be four editors divided into two groups

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]

I took a quick look for the moment at the PR and I believe the commit 79da67b should be squashed since it is simply fixing an issue from a previous commit of the same pull request.

---

I tried and it looks like it works correctly, here are my results when running on master:

and using your pull request:

[godlin-gh]

I took a quick look for the moment at the PR and I believe the commit 79da67b should be squashed since it is simply fixing an issue from a previous commit of the same pull request.

I tried and it looks like it works correctly, here are my results when running on master:

and using your pull request:

I've squashed that two commits now.

[akosyakov]

@godlin-gh very good job! code changes look good, thanks @vince-fugnitto for testing!