monaco: restore drop-shadow for quick-input

[vince-fugnitto]

What it does

The commit updates the styling of the quick-input to restore the drop-shadow which was previously present (and present in vscode) following the monaco upgrade. The drop-shadow helps to display the overlay especially when there is content behind such as an editor, and it aligns with our previous styling and that of vscode.

before:

drop-before.mov

after:

drop-after.mov

How to test

1. start the application, and trigger a quick-input (ex: F1)
2. confirm that the quick-input has a drop-shadow applied, similarly to vscode and that master did not
3. confirm the same for quick-pick (ex: run task...)

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

Signed-off-by: vince-fugnitto [email protected]

[msujew]

Looks good to me 👍 Tested with different color themes and couldn't notice any visual difference to vscode.