Add convenience methods for fetching nodes deep in the tree

[eslavich]

This adds convenience methods for fetching nodes deep in the tree. For example, until now it has been necessary to chain method calls to get to a node at path root.child.grandchild:

node.get("root").get("child").get("grandchild")

This PR adds vararg overloads of the get methods so that this can be accomplished in a single method call:

node.get("root", "child", "grandchild")

Since varargs can't be followed by other arguments, I'm also deprecating the old getList and getMap methods and introducing new methods that place the list and map types at the beginning of the argument list.

Thanks Trey for the idea!

[github-actions]

Overall Project	57.82% -0.49%	🍏
Files changed	88.71%	🍏

Module	Coverage
asdf-core	57.88% -0.5%	🍏

Files

Module	File	Coverage
asdf-core	NumberAsdfNode.java	97.6% -1.54%	🍏
	ReferenceFileUtils.java	85.85% -0.98%	🍏
	AsdfNodeBase.java	63.88% -4.4%	🍏

[robyww]

This looks good. I think it will make the library easier to use. thanks!.

[alphasentaurii]

This looks good - appreciate the added test case for this as well. Thanks Ed!

[github-actions]

Overall Project	57.82% -0.49%	🍏
Files changed	88.71%	🍏

Module	Coverage
asdf-core	57.88% -0.5%	🍏

Files

Module	File	Coverage
asdf-core	NumberAsdfNode.java	97.6% -1.54%	🍏
	ReferenceFileUtils.java	85.85% -0.98%	🍏
	AsdfNodeBase.java	63.88% -4.4%	🍏