Hide the sash when the left/right side panel is collapsed and when the horizontal container is collapsed

[kaiyue0329]

What it does

• Hide the sash when the left/right side panel is collapsed (see the two videos for comparison)

before.mov

now.mov

• Fix bug for the scenario in the left panel where the sash is visible when all horizontal containers are collapsed (please refer to the screenshot below for more details)

Before	After

How to test

1. Verify that the sash is hidden when the left/right side panel is collapsed
2. Verify that the sash for the left/right side panel functions properly (try updating its size and hoverDelay)
3. Install GitLens or Maven for Java extension from the VSX Registry (GitLens is used in the screenshot above)
4. Locate a horizontal container for the extension from the left panel. Without clicking on the horizontal container, verify that the sash is hidden when the container is collapsed

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

[msujew]

Looks good to me!

• No sash appears, when the side panel is hidden (left/right)
• Sashes on view containers only appear when the container above is expanded.

I have a minor comment, but aside from that it looks good to go.

[vince-fugnitto]

The changes work well for me 👍

• confirmed that the sash does not display if the view is hidden in sidepanels
• confirmed that the sash correctly displays if the view is not hidden in sidepanels
• confirmed that there are no visible regressions

[JonasHelming]

@vince-fugnitto @msujew : I think we can merge this!?

[msujew]

@JonasHelming Thanks for the heads-up, I merged it!