Remove error-prone source_id from TypeEngine::insert() and make inserting API more robust and less verbose

[ironcev]

In the TypeEngine::insert() method, the source_id parameter makes sense and should be provided only for the types that can actually be defined in source files, e.g., TypeInfo::Enum or TypeInfo::Struct. Actually, for such types it must be provided in order for garbage collection to work properly.

For types like e.g. TypeInfo::Array the source_id makes no sense as well as for all the built in types. E.g. calling te.insert(engines, TypeInfo::Numeric, some_span.source_id()) makes no sense.

The current signature of insert() is quite error-prone in that regard and verbose in many cases (e.g. inserting built-in types). The caller has to choose the valid source_id (or None) although the choice is actually determined by the type being inserted. E.g. if we are inserting an enum the source_id must always come from the enum decl span. Currently, since we are inserting same types at various places, it is only the convention that makes the source_id always the same.

Also, we have places in code where source_id should be None (inserting TypeInfo::Array for example) but it is set to a value (source of the array element span in that particular case, although it makes no sense).

Therefore, the proposal is to make the insert() API secure in regard to source_id and less verbose at the same time by:

• removing source_id it from the insert() method and infer it based on the inserted type.
• provide robust and secure support for the autogenerated source files (engines.se().get_autogenerated_source_id(module_id))
• provide convenience methods for inserting common types like Unknown or built-in types.