Add foam.DEF_MACRO and foam.APPLY_MACRO

[KernelDeimos]

Meta-programming is already possible in FOAM by calling methods like foam.CLASS dynamically. This PR introduces explicit meta-programming support so that this behavior can be better controlled by FOAM.

The following example defines a macro that creates two models for each value it's applied to:

foam.DEF_MACRO({
  package: 'com.example',
  name: 'ExampleMacro',
  
  code: function (name) {
    foam.CLASS({
      package: 'com.example',
      name: 'Greedy' + name
    });
    foam.CLASS({
      package: 'com.example',
      name: 'Lazy' + name
    });
  }
});

We can then imply models GreedyCat, LazyCat, GreedyDog and LazyDog as follows:

foam.APPLY_MACRO('com.example.ExampleMacro', ['Cat', 'Dog']);

In order to justify adding explicit support, the need for meta-programming is a prerequisite justification. Sometimes it makes sense to generate individual models from tabular data in a similar fashion that FOAM can already generate models from XSD files. I came across a good example while modelling WebAssembly functions. Each instruction has different properties and creating a general model to handle all cases would add complexity and prevent adding refinements to individual instructions.

With foam.APPLY_MACRO I was able to represent the differences between instructions concisely in a few lines of code:

foam.APPLY_MACRO("wasm.ins.InstructionMacro", [
    [0x25,     'table.get',  'idx:u32'],
    [0x26,     'table.set',  'idx:u32'],
    [0xFC, 12, 'table.init', 'elemIdx:u32', 'tableidx:u32'],
    [0xFC, 13, 'elem.drop',  'idx'],
    [0xFC, 14, 'table.copy', 'a:u32', 'b:u32'],
    [0xFC, 15, 'table.grow', 'idx:u32'],
    [0xFC, 16, 'table.size', 'idx:u32'],
    [0xFC, 17, 'table.fill', 'idx:u32'],
]);

Here are some advantages of explicit support as opposed to the meta-programming that is already possible:

• Explicit support makes it easy to spot. When you see _MACRO, you know meta-programming is happening.
• Generated models can be handled differently by code generators if needed.
• Helpful axioms like documentation can be added to the macro itself

[kgrgreer]

Explicit support makes it easy to spot. When you see _MACRO, you know meta-programming is happening.
It's FOAM, meta-programming is always happening.
I'm not convinced that this is worth adding.