This fixes an issue that Touch Keyboard is not invoked when user taps on the PowerShell.
Before this change, it was returning small rectangle on the right of the cursor. Touch Keyboard should be invoked by tapping anywhere inside the console.
## PR Checklist
* [ ] Closes #xxx
* [x] CLA signed. If not, go over [here](https://cla.opensource.microsoft.com/microsoft/Terminal) and sign the CLA
* [ ] Tests added/passed
* [ ] Documentation updated. If checked, please file a pull request on [our docs repo](https://github.com/MicrosoftDocs/terminal) and link it here: #xxx
* [ ] Schema updated.
* [x] I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx
## Detailed Description of the Pull Request / Additional comments
ITfContextOwner::GetScreenExt is used to define rectangle that can invoke Touch Keyboard.
https://docs.microsoft.com/en-us/windows/win32/api/msctf/nf-msctf-itfcontextowner-getscreenext
## Validation Steps Performed
* [x] Touch keyboard was invoked by tapping inside the Console while Hardware Keyboard was not attached.
* [x] Selecting text worked as expected without invoking touch keyboard.
* [x] Long tapping the console invoked Touch Keyboard. I would like to confirm if this is the expected behavior.
