Use update boolean instead of hard set 'true' in modelsource submitModel

[jbicker]

Before setModel always ended up in UpdateModelAction which triggers (in that case) unwanted animations.

[spoenemann]

Remark: the constant true value was originally used to keep the previous behavior in #103. The unexpected behavior should be fixed. If you want the model change to be animated, use updateModel.

[spoenemann]

For reference: the reason for the constant true value was that before the introduction of the request/response scheme, there was no easy way to retain the value of that flag during the bounds computation phase:

sprotty/src/model-source/local-model-source.ts

Lines 238 to 255 in de20406

	protected handleComputedBounds(action: ComputedBoundsAction): void {
	const root = this.currentRoot;
	const index = new SModelIndex();
	index.add(root);
	for (const b of action.bounds) {
	const element = index.getById(b.elementId);
	if (element !== undefined)
	this.applyBounds(element, b.newBounds);
	}
	if (action.alignments !== undefined) {
	for (const a of action.alignments) {
	const element = index.getById(a.elementId);
	if (element !== undefined)
	this.applyAlignment(element, a.newAlignment);
	}
	}
	this.doSubmitModel(root, true, index);
	}