Add support for new grid layout with splits

[rodcloutier]

** Feature request **

Split command should support the upcoming grid layout feature from VsCode.

VsCode issue and PR:

• Support a grid layout for editors microsoft/vscode#14909
• Implement a grid editor layout feature microsoft/vscode#49599

[jpoon]

Closed with #2697

[elviskahoro]

@rodcloutier @jpoon I typically use +s or +v to create split panes. It stopped working for me so wanted to double check that this wasn't happening for others.

:vs still works!

[jwtly10]

@rodcloutier @jpoon I typically use +s or +v to create split panes. It stopped working for me so wanted to double check that this wasn't happening for others.

:vs still works!

This has also stopped working for me!