Implement fluent parser & start migration

[Pablete1234]

For a long while, PGM has had an explosion of parsing methods to support the different ways in which we can parse. Overloads upon overloads for parsing a node, an element, an attribute, required or with a default, maybe with a validation in there too.

That doesn't create the cleanest programming model, and it's why i want to move away from it. Welcome fluent parsing api:

// Before (yes, all diff 10  overloads exist for filters):
var a1 = parseProperty(el, "filter"); // Defaults to null, non-obvious
var b1 = parseProperty(el, "filter", StaticFilter.ALLOW); // Defaults to ALLOW
var c1 = parseProperty(el, "filter", DynamicFilterValidation.ANY); // Defaults to null, non-obvious
var d1 = parseProperty(el, "filter", StaticFilter.ALLOW, DynamicFilterValidation.ANY);

var a2 = parseProperty(Node.fromChildOrAttr(el, "filter", "trigger"));
var b2 = parseProperty(Node.fromChildOrAttr(el, "filter", "trigger"), StaticFilter.ALLOW);
var c2 = parseProperty(Node.fromChildOrAttr(el, "filter", "trigger"), DynamicFilterValidation.ANY);
var d2 = parseProperty(Node.fromChildOrAttr(el, "filter", "trigger"), StaticFilter.ALLOW, DynamicFilterValidation.ANY);

var a3 = parseRequiredProperty(el, "filter");
var b3 = parseRequiredProperty(el, "filter", DynamicFilterValidation.ANY);

// After
var a1 = parser.filter(el, "filter").orNull();
var b1 = parser.filter(el, "filter").orAllow();
var c1 = parser.filter(el, "filter").dynamic().orNull();
var d1 = parser.filter(el, "filter").dynamic().orAllow();

var a2 = parser.filter(el, "filter", "trigger").orNull();
var b2 = parser.filter(el, "filter", "trigger").orAllow();
var c2 = parser.filter(el, "filter", "trigger").dynamic().orNull();
var d2 = parser.filter(el, "filter", "trigger").dynamic().orAllow();

var a3 = parser.filter(el, "filter").required();
var b3 = parser.filter(el, "filter").dynamic().required();

This is just a specific example for filters (listing all 10 former methods) but the new api also comes with more methods like optional(defaultValue) of which orAllow is just an overload specifically for filters. The beauty is we can compose these calls without having an explosion in method overloads.