Test: API changes for grid editor layout

[bpasero]

Refs: #51001

• any os @sbatten
• any os @roblourens

Complexity: 3

There are some slight changes to the API to support grid editor layout. The ViewColumn is mapped onto the grid in a way that it represents the order of grid views in the grid (e.g. 1, 2, 3 for a 3 column layout from left to right, see docs). This is to stay compatible with how it used to be before when we only supported up to 3 columns. Verify:

• Verify textEditor.viewColumn is always defined for an editor in the grid even if many are opened
• Verify onDidChangeTextEditorViewColumn is fired when a group disappears to the left of the editor (so that its view column changes) or when moving a group to another location with drag and drop (drag the entire group, not just the tab!)
• Verify ViewColumn.Beside can be used to always open an editor to the side (*)
• Verify the vscode.setEditorLayout can be used to set an editor layout

(*): pull in our vscode.d.ts from master to get it