Feature request: support BasicObject variables

[amomchilov]

Subclasses of BasicObject are rare in general, but pretty common in testing/mocking frameworks.

Today, the logic in print_variable will raise NoMethodError for such objects, and always hit this rescue:

ruby-debug-ide/lib/ruby-debug-ide/xml_printer.rb

Lines 310 to 312 in 3a74a47

	print_debug "Unexpected exception \"%s\"\n%s", e.to_s, e.backtrace.join("\n")
	print("<variable name=\"%s\" kind=\"%s\" value=\"%s\"/>",
	CGI.escapeHTML(name), kind, CGI.escapeHTML(safe_to_string(value)))

You can see this other PR of mine to see what's involved, but in short:

1. Replacing object.is_a?(Foo) with Foo === object
2. Replacing object.to_s with Kernel.instance_method(:to_s).bind_call(object)

Before I try this, would this be a welcome contribution to merge?