add Text.letterSpacing typescript definitions

Also fixed the JSDoc type

Author: Akurn

src/gameobjects/Text.js

@@ -2098,7 +2098,7 @@ Object.defineProperty(Phaser.Text.prototype, 'lineSpacing', {
 
 /**
  * @name Phaser.Text#letterSpacing
- * @property {number} letterSpacing - Additional spacing between letters in CSS [length]{@link https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Values/length} units.
+ * @property {string} letterSpacing - Additional spacing between letters in CSS [length]{@link https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Values/length} units.
  * Uses [CanvasRedneringContext2D.letterSpacing]{@link https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/letterSpacing} property.
  */
 Object.defineProperty(Phaser.Text.prototype, 'letterSpacing', {

typescript/phaser.d.ts

@@ -5140,6 +5140,7 @@ declare module Phaser {
         wordWrap?: boolean;
         wordWrapWidth?: number;
         maxLines?: number;
+        letterSpacing?: string;
         shadowOffsetX?: number;
         shadowOffsetY?: number;
         shadowColor?: string;
@@ -5197,6 +5198,7 @@ declare module Phaser {
         game: Phaser.Game;
         input: Phaser.InputHandler;
         inputEnabled: boolean;
+        letterSpacing: string;
         lineSpacing: number;
         name: string;
         padding: Phaser.Point;