Add support for Relu activation as Elementwise op

[SpiritSeeker]

Implements Relu as an elementwise op. The following changes are introduced:

• add ElementwiseMax op (fixed-point support depends on Add fixed-point support for elementwise operations #1445)
• add additional test for ElementwiseMax
• infer Relu as ElementwiseMax
• add tests for Relu with integer, FP32, FP16, and fixed-point inputs.

[auphelia]

This PR introduces a ReLU implementation built on top of the existing elementwise binary ops.
There is a separate WIP PR (#1500) from @SpiritSeeker that will provide a more direct ReLU operation without requiring the second input to be a constant. Once that PR is ready, it will supersede the implementation introduced here.
In the meantime, we are merging this PR to enable conversion of standalone ReLUs to hardware and unblock current workflows.