Add window resize "sash" options

[kenneth-marut-work]

For some users (including those working through a remote desktop client with latency) it can be quite hard to resize windows & view containers as the mouse target size for resize handles is quite small. VSCode has a feature called workbench "sash" that applies focus to borders as you drag over them. VSCode also implements 2 preferences to customize this behavior (hover delay and size):

This would be a really nice feature to have