fix wrong function name of TS def (the correct names are in index.js)

Author: jcyuan

src/math/pow2/GetPowerOfTwo.js

@@ -7,7 +7,7 @@
 /**
  * Returns the nearest power of 2 to the given `value`.
  *
- * @function Phaser.Math.Pow2.GetPowerOfTwo
+ * @function Phaser.Math.Pow2.GetNext
  * @since 3.0.0
  *
  * @param {number} value - The value.

src/math/pow2/IsSizePowerOfTwo.js

@@ -8,7 +8,7 @@
  * Checks if the given `width` and `height` are a power of two.
  * Useful for checking texture dimensions.
  *
- * @function Phaser.Math.Pow2.IsSizePowerOfTwo
+ * @function Phaser.Math.Pow2.IsSize
  * @since 3.0.0
  *
  * @param {number} width - The width.

src/math/pow2/IsValuePowerOfTwo.js

@@ -7,7 +7,7 @@
 /**
  * Tests the value and returns `true` if it is a power of two.
  *
- * @function Phaser.Math.Pow2.IsValuePowerOfTwo
+ * @function Phaser.Math.Pow2.IsValue
  * @since 3.0.0
  *
  * @param {number} value - The value to check if it's a power of two.