Grid: when opening a 2x2 grid existing editors are misplaced

[stevencl]

Issue Type: Bug

Open two files side by side
View -> Editor Layout -> Grid 2x2
Note that the editor that was on the right hand side is now underneath the other editor.
Expected both editors to remain positioned side by side on the top row with two empty cells underneath each in the second row

This is made a little worse by the fact that when you then drag the editor from the bottom left to the top right, the group in the bottom left is closed.

VS Code version: Code - Insiders 1.25.0-insider (368ab9c, 2018-06-26T05:18:23.085Z)
OS version: Windows_NT x64 10.0.16299

System Info

Item	Value
CPUs	Intel(R) Core(TM) i7-3687U CPU @ 2.10GHz (4 x 2594)
GPU Status	2d_canvas: enabled flash_3d: enabled flash_stage3d: enabled flash_stage3d_baseline: enabled gpu_compositing: enabled multiple_raster_threads: enabled_on native_gpu_memory_buffers: disabled_software rasterization: disabled_software video_decode: enabled video_encode: enabled vpx_decode: unavailable_software webgl: enabled webgl2: enabled
Memory (System)	7.89GB (1.08GB free)
Process Argv	C:\Program Files\Microsoft VS Code Insiders\Code - Insiders.exe
Screen Reader	no
VM	0%

Extensions (15)

Extension	Author (truncated)	Version
html-snippets	abu	0.2.1
jshint	dba	0.10.19
vscode-eslint	dba	1.4.12
tslint	eg2	1.0.33
vscode-great-icons	emm	2.1.35
vscode-gutter-preview	kis	0.12.2
vscode-azureappservice	ms-	0.8.1
vscode-cosmosdb	ms-	0.7.2
azure-account	ms-	0.4.1
csharp	ms-	1.15.2
vs-keybindings	ms-	0.2.0
team	ms-	1.136.0
debugger-for-chrome	msj	4.7.0
addDocComments	ste	0.0.8
cordova-tools	vsm	1.4.0


Found while testing: #52334

[bpasero]

This depends a little bit on the root orientation and might be hard to get right, but I am willing to look into this to see if there is something lowhanging we can do.

/cc @joaomoreno

[joaomoreno]

@bpasero Maybe we can preserve the original orientation?