schema: complete validation

[kristoff-it]

In the construction of a Schema struct, we currently check for:

• Duplicate tag literal definitions
• Usage of unknown tag literals
• Duplicate struct definitions
• Duplicate struct field
• Usage of unknown struct names
• Duplicate mentions of the same Struct inside of a struct union expression

What's missing:

• Recognizing types of infinite size (ie self-references outside of a map or array container)
• Recognizing definitions impossible to reach from the root expression

Note that the presence of any automatically colors everything.

How to get started

Here we perform the aforementioned analysis:

ziggy/src/schema/Schema.zig

Lines 168 to 176 in 4905290

	log.debug("beginning analysis", .{});
	try schema.analyzeRule(gpa, schema.root, nodes, code, diagnostic);
	log.debug("root_rule analized", .{});
	for (schema.structs.keys(), schema.structs.values()) |s_name, s| {
	for (s.fields.keys(), s.fields.values()) |f_name, f| {
	log.debug("analyzeRule '{s}.{s}'", .{ s_name, f_name });
	try schema.analyzeRule(gpa, f.rule, nodes, code, diagnostic);
	}
	}

Below those lines it would make sense to call a new function that performs the remaining checks.
It might make sense to add a field or two to the existing types (eg StructRule, Rule).