Fix prettyprinting in C API

[jemmaissroff]

We have done a lot of work to make the pretty printing look nice in the Ruby API. We should mirror this in the pm_print_node function in the C API so that C can also benefit from the nice printing

[eregon]

FWIW there is also pretty printing for Java which is sort of similar to the Ruby one but much simpler:

prism/templates/java/org/prism/Nodes.java.erb

Lines 279 to 326 in f7ff3a3

	@Override
	protected String toString(String indent) {
	StringBuilder builder = new StringBuilder();
	builder.append(this.getClass().getSimpleName());
	if (hasNewLineFlag()) {
	builder.append("[Li]");
	}
	builder.append('\n');
	String nextIndent = indent + " ";
	<%- if node.fields.any?(Prism::NodeListField) or node.fields.any?(Prism::ConstantListField) -%>
	String nextNextIndent = nextIndent + " ";
	<%- end -%>
	<%- node.fields.grep_v(Prism::LocationField).grep_v(Prism::OptionalLocationField).each do |field| -%>
	builder.append(nextIndent);
	builder.append("<%= field.name %>: ");
	<%- case field -%>
	<%- when Prism::NodeField -%>
	builder.append(this.<%= field.name %>.toString(nextIndent));
	<%- when Prism::OptionalNodeField -%>
	builder.append(this.<%= field.name %> == null ? "null\n" : this.<%= field.name %>.toString(nextIndent));
	<%- when Prism::NodeListField -%>
	builder.append('\n');
	for (Node child : this.<%= field.name %>) {
	builder.append(nextNextIndent).append(child.toString(nextNextIndent));
	}
	<%- when Prism::StringField -%>
	builder.append('"' + new String(this.<%= field.name %>, StandardCharsets.UTF_8) + '"');
	builder.append('\n');
	<%- when Prism::ConstantField -%>
	builder.append('"').append(this.<%= field.name %>).append('"');
	builder.append('\n');
	<%- when Prism::OptionalConstantField -%>
	builder.append(this.<%= field.name %> == null ? "null" : "\"" + this.<%= field.name %> + "\"");
	builder.append('\n');
	<%- when Prism::ConstantListField -%>
	builder.append('\n');
	for (<%= string_type %> constant : this.<%= field.name %>) {
	builder.append(nextNextIndent).append('"').append(constant).append('"').append('\n');
	}
	<%- when Prism::UInt32Field, Prism::FlagsField -%>
	builder.append(this.<%= field.name %>);
	builder.append('\n');
	<%- else -%>
	<%- raise field.class.name -%>
	<%- end -%>
	<%- end -%>
	return builder.toString();
	}

That might be a good fit for C and easier to port than the more complex logic used in Ruby.