[Feature] Document impact of Solidity item visibility

[DaniPopes]

Component

sol! macro

Describe the feature you would like

Currently this is ignored, except for state variables:

core/crates/sol-macro/src/expand/mod.rs

Lines 267 to 282 in c8dece2

	fn visit_items(items: &mut Vec<Item>) {
	// add a getter function for each public variable
	let mut functions = Vec::new();
	for (i, item) in items.iter().enumerate() {
	match item {
	Item::Variable(var) => {
	if matches!(
	var.attributes.visibility(),
	Some(ast::Visibility::Public(_) | ast::Visibility::External(_))
	) {
	functions.push((i + 1, ItemFunction::from_variable_definition(var)));
	}
	}
	_ => {}
	}
	}

Additional context

• Should we ignore it always?
• Should we also take it into account for functions and other items?
  cc @prestwich