add type annotation to onLocationChange about niivue

[neurolabusc]

@thangngoc89 this is a good start. Here is a screenshot of the structure:

Therefore, I think the full description is:

type NiiVueLocationValue = {
  id: string;
  mm: Float32Array;
  name: string;
  value: number;
  vox: [number, number, number];
};
type NiiVueLocation = {
  axcorsag: number;
  frac: Float32Array;
  mm: Float32Array;
  string: string;
  values: NiiVueLocationValue[];
  vox: Float32Array;
  xy: [number, number];
};

At first inspection, the fact that vox and mm are reported for both the main structure and separately for each layer. However, it is worth noting that all overlays are resliced to match the resolution and field-of-view of the background image. Therefore, due to interpolation, rotation and zoom, the overlays are often different from the background image.

[thangngoc89]

This is from my project's code snippet. You can use it as a starting point. Public domain license.

type NiiVueLocationValue = {
  id: string;
  mm: Float32Array;
  name: string;
  value: number;
  vox: [number, number, number];
};
type NiiVueLocation = {
  vox: [number, number, number];
  string: string;
  values: NiiVueLocationValue[];
};