Mark TextMetrics#fontBoundingBoxAscent etc. as unimplemented

[DiamondMofeng]

Issue

I have some need to measure the height of fonts.
But TextMeasure.fontBoundingBoxAscent is always undefined.

It seems that these API are not implemented.
However, the typescript definition provides the relevant definitions.

Maybe it's better to mark these API as unimplemented.

Steps to Reproduce

var Canvas = require('canvas');
var canvas = Canvas.createCanvas(200, 200);
var ctx = canvas.getContext('2d');

ctx.font = "Arial";
const measure = ctx.measureText('test');

console.log(measure.fontBoundingBoxAscent); // undefined;
console.log(measure); 
/*
{
  width: 16.416015625,
  actualBoundingBoxLeft: -1,
  actualBoundingBoxRight: 17.0712890625,
  actualBoundingBoxAscent: 7,
  actualBoundingBoxDescent: 0,
  emHeightAscent: 11,
  emHeightDescent: 3,
  alphabeticBaseline: 1
}
*/

Your Environment

• Version of node-canvas (output of npm list canvas or yarn list canvas): canvas 2.11.2
• Environment (e.g. node 20.9.0 on macOS 14.1.1): node v18.18.2

[Crysp]

+1 same issue