ViewHelper: Make label text and style configurable.

[puxiao]

Added label text to display configuration items.

#28312 (comment)

class ViewHelper extends Object3D {
-  constructor( camera: Camera, domElement: HTMLElement );
+  constructor( camera: Camera, domElement: HTMLElement, options?: ViewHelperOptions );
}

export interface ViewHelperOptions {
    font?: string  //default value: '24px Arial'
    labelColor?: string //default value: '#000000'
    posXLabel?: string //default value: null (no display)
    posYLabel?: string
    posZLabel?: string
    radius?: number //default value: 14
}

If you want bold text :

{
-   font: '24px Arial',
+   font: 'Bold 24px Arial',
    posXLabel: 'X',
    posYLabel: 'Y',
    posZLabel: 'Z',
}

If you want to display in Chinese :

const viewHelper = new ViewHelper( camera, renderer.domElement, {
    posXLabel: '右',
    posYLabel: '上',
    posZLabel: '前',
    font: 'Bold 24px Arial',
    labelColor: '#000000',
    radius: 20,
} )