Reflective structures

[lukebemish]

Adds an API for constructing structures reflectively from a class. For instance:

public record TestRecord(int a, String b, TestEnum c) {
    public static final Structure<TestRecord> STRUCTURE = ReflectiveStructureCreator.create(TestRecord.class);
}

public enum TestEnum {
    A,
    B,
    C
}

TODO:

• Add support for annotations from gson/others
• Support optional/nullable fields
• Add annotations specific for structures, such a pointing a given field at a particular structure.
• Add annotations for comments and the like
• Look into groovy support, including retrieving groovydoc
• Self referencing classes
• Caching (probably relevant to self referencing classes)
• Add recursive structure support to remaining interpreters, with tests
• Write docs
• Make tests more comprehensive
• Handle reified generic records
• Allow contextual specification of method handles (currently uses MethodHandles.lookup() throughout) and test in modular environment

[lukebemish]

Recursion is going to be something that may take a bit -- turns out normal Structures don't support it in all cases at present. Got structures to support them, and then just propogated that system to the reflective system.

[lukebemish]

Turns out commented codecs broke at some point, and I discovered while writing tests for reflective structures with comments! Well, this is what we have tests for -- added some more for commented codecs in particular.

[lukebemish]

Groovy groovydoc detection and use is supported through a small class that bounces to an implementation at present -- is this my favorite? No. It only works if groovy is visible from codecextras's classloader -- which in different-module-layer cases might not, I suppose, be the case. This may be expanded if I ever end up making a specific codecextras-groovy module -- I'll just move it there as a service implementer.

[lukebemish]

Also working on mutable data representation for structures -- which adds a few more renames/refactors for the next time I do BCs. Not sure if there's a sensible way to hook those up reflectively, and I may not bother -- the proper API there is almost certainly direct use of DataElements and types.