src/vs/workbench/contrib/terminal/browser/terminalEditorService.ts/TerminalEditorService/splitInstance
class TerminalEditorService:	splitInstance(instanceToSplit: ITerminalInstance, shellLaunchConfig: IShellLaunchConfig = {}): ITerminalInstance {
		if (instanceToSplit.target === TerminalLocation.Editor) {
			// Make sure the instance to split's group is active
			const group = this._editorInputs.get(instanceToSplit.resource.path)?.group;
			if (group) {
				this._editorGroupsService.activateGroup(group);
			}
		}
		const instance = this._terminalInstanceService.createInstance(shellLaunchConfig, TerminalLocation.Editor);
		const resource = this.resolveResource(instance);
		if (resource) {
			this._editorService.openEditor({
				resource: URI.revive(resource),
				description: instance.description,
				options: {
					pinned: true,
					forceReload: true
				}
			}, SIDE_GROUP);
		}
		return instance;
	}