Grid: Support adding horizontal split below a vertical split

[qcz]

Issue Type: Bug

If I have two vertically splitted editors like this:

___________
|    |    |
|    |    |
|____|____|

I want to be able to move an editor below these to to create a horizontal split like this:

___________
|    |    |
-----------
|_________|

But I cannot do that:

The editor supports this kind of layout, because if I create a horizontal split first, and split the upper horizontal, I can create the desired layout:

This is why I wonder why it is not possible to create this layout using the first method.

VS Code version: Code - Insiders 1.24.0-insider (0f4cde3, 2018-06-01T12:17:19.366Z)
OS version: Windows_NT x64 10.0.16299

Extensions (10)

Extension	Author (truncated)	Version
xml	Dot	2.2.0
tslint	eg2	1.0.30
vscode-great-icons	emm	2.1.33
vscode-todo-plus	fab	2.1.2
vscode-insiders-language-pack-hu	MS-	1.23.1
mssql	ms-	1.3.1
debugger-for-chrome	msj	4.5.0
polacode	pnp	0.2.2
vscode-icons	rob	7.23.0
markdown-pdf	yza	1.2.0

(3 theme extensions excluded)

[vscodebot]

(Experimental duplicate detection)
Thanks for submitting this issue. Please also check if it is already covered by an existing one, like:

• Grid: weird resize behaviour when closing empty group (#50564)
• vertical/horizontal split window (#24998)
• Allow split editor keyboard shortcut for horizontal and vertical (#50431)
• Allow to split an editor into two without creating separate tabs (#36700)
• Feature Request: Split Editors both Horizontally and Vertically (#50961)

[aeschli]

duplicate of #50666