Refactor math_ops.cu dispatcher logic

[davidwendt]

Description

Refactors the type-dispatcher logic and cleans up the code in math_ops.cu for unary operations.
The 3 of the 4 dispatch functors had the same logic except for the supported types SFINAE clause.
Also correcting the code for handling RINT properly created a 4th common functor.
These have been refactored into a single functor and separated from the supported-types checks.
The single functor now excepts the transform function as well as the supported-types expression.
Also, the 2nd dispatcher call for dictionary was replaced with an if-statement to help simplify the code and minimize maintenance syncing up the supported-types clauses correctly.

One side effect is that more ops are now supported appropriately with dictionary types.

Referenced cleanup needed here: #17560 (comment)

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[Matt711]

FWIW changes look good.