Customize test failure display

[jariji]

I like how it shows the values of y and x here

julia> @test y < x
Test Failed at REPL[6]:1
  Expression: y < x
   Evaluated: 2 < 1

I would like to make it do that for custom functions.

julia> eq(x,y) = x == y;

julia> @test eq(x,y)
Test Failed at REPL[5]:1
  Expression: eq(x, y)

A few options are presented on Discourse but they all require intervention by the tester at the test site.

I want to customize the error display by dispatching on the predicate function and/or its arguments. So for my custom eq and maybe its argument types I could get

julia> @test eq(x,y)
Test Failed at REPL[5]:1
Expression eq(x,y)
  Evaluated eq(1,2)

and other predicates could define other displays.

[giordano]

Related: #55409