The `ComponentReader` should not require the component byte length

[javagl]

The ComponentReader is returned by a function that receives the componentType, and it is, in turn, a function that receives (among other things) the componentTypeByteLength. This is not necessary. It can be determined from the componentType that is passed in.

When updating this, the use of this class in CesiumJS has to be taken into account (i.e. that would be a "breaking change", despite the @private...)