Wrong names of RAD_PER_DEG and DEG_PER_RAD constants

[ikokostya]

Math.RAD_PER_DEG and Math.DEG_PER_RAD constants have invalid names in the current spec:

• Math.RAD_PER_DEG is equal to 180 / PI, but must be equal PI / 180, because this constant means radians in one degree. Also Math.radians(degrees) must be computed as

  - 2. Let radians be (degrees × Math.DEG_PER_RAD).
  + 2. Let radians be (degrees × Math.RAD_PER_DEG).

• Accordingly Math.DEG_PER_RAD must be equal 180 / PI, because it means number of degrees in one radian, and Math.degrees(radians) must be computed as:

  - 2. Let degrees be (radians × Math.RAD_PER_DEG).
  + 2. Let degrees be (radians × Math.DEG_PER_RAD).

Looks like this issue was introduced in the following commit b31aee6