Add view container resize sash options

[kaiyue0329]

What it does

Fix: #10416

• Apply focus to the widget borders when you hover over them
• sash.hoverDelay controls the hover feedback delay in milliseconds
• sash.size controls the feedback area size in pixels for the dragging area
• Add preference to set workbench.sash.hoverDelay (value must in the range of 1 to 2000, default is 1ms)
• Add preference to set workbench.sash.size (value must in the range of 1 to 20, default is 7px)

sash-option.mov

How to test

1. Start the application
2. Hover the cursor over the horizontal and vertical borders for different view containers in Theia and drag (please refer to the screencast above for more details)
3. Search for 'workbench sash' in Preferences (File > Preferences > Open Settings (UI) )
4. Update the sash.hoverDelay and sash.size preferences to valid values
5. Repeat Step 2 and verify that the hover delay and feedback area size for the border/sash are updated successfully

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