[SPARK-19733][ML] Removed unnecessary castings and refactored checked casts in ALS.

## What changes were proposed in this pull request?

The original ALS was performing unnecessary casting to the user and item ids because the protected checkedCast() method required a double. I removed the castings and refactored the method to receive Any and efficiently handle all permitted numeric values.

## How was this patch tested?

I tested it by running the unit-tests and by manually validating the result of checkedCast for various legal and illegal values.

Author: Vasilis Vryniotis <bbriniotis@datumbox.com>

Closes #17059 from datumbox/als_casting_fix.