quick-input: alter styling of codicon to resemble vscode

[Archie27376]

What it does

Fixes #10389

This commit alters the appearance of the codicons that show in the Run Task menu to be similar to vscode.
The color has been changed from blue to one that follows the present color theme.
The background of the icon when hovering over is now a square and centered around the icon to be more aesthetically pleasing.

How to test

• Start the application using theia as a workspace
• Execute the command Run Task using F1
• Hover over each task to notice the tail icon colored correctly with the theme
• Hover over the tail icon for the hover background

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

[colin-grant-work]

The changes improve the theming, and I don't see any regressions.