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.