Add ability to use atan2 and hypot functions with fp16 arguments.

Description

Cases have been added to the atan2 and hypot functions to handle fp16 arguments. Previously an exception was thrown when trying to use fp16 arguments with these functions.

Tests have been added to verify that these functions are working correctly with fp16 arguments. Note that the OpenCL back end does not support half precision.

Several other functions have been identified as not supporting fp16, a new issue will be created for these.

Fixes: #3545

Changes to Users

atan2 and hypot functions can now be used on fp16 arrays

Checklist

• [ x] Rebased on latest master
• [ x] Code compiles
• [ x] Tests pass
• [ x] Functions added to unified API
• [ x] Functions documented