Add new get_stack function to get GDScript stack trace as array

[chanon]

As an alternative or addition to #18966, this adds a new function get_stack() that returns the stack trace as an array that looks like:

[
	{ "source": "res://path/to/file.gd", "function": "_name_of_function_a", "line": 34 },
	{ "source": "res://path/to/file.gd", "function": "_name_of_function_that_called_function_a", "line": 45 }
]

This allows creation of custom print/debugging/tracing/logging methods with custom formats in GDScript.

Implements #13335

[chanon]

Just to show how I've used the get_stack method in this pull request to create a customized print method:

With a print method that looks like this:

func debug(text):
	var frame = get_stack()[1]
	print( "%30s:%-4d %s" % [frame.source.get_file(), frame.line, text] )

My Output window logs now look like this:

With ability to customize and get additional debug info, I think this will greatly help with productivity.

[chanon]

Actually, another option (or another thing that could be added) is to expose the debug_get_stack_level_xxx methods directly to GDScript. But it isn't clear how/where they should be exposed as I don't think GDScriptLanguage::get_singleton is exposed to GDScript.

This get_stack method is still convenient though and is a good alternative to print_stack