…forward references
Improve forward reference resolution in template instantiation with alias
- Check needGagging in TemplateInstance::semantic2()
- Set TemplateInstance::speculative if global.gag is set in semantic()

…regate members
It would cause unresolved forward reference because `TypeStruct::hasPointers()` requires the complete types of the fields.

By the improvement of recursive aliasing, we can simplify the concept to:
"A template instantiation during errors gagged is 'speculative instantiation'".

Issue 13333 - Incorrect error ungagging during the resolution of forward references

Issue 13333 - Incorrect error ungagging during the resolution of forward references

* [spec/memory-safe-d] Improve `return` attribute docs
Fix Bugzilla 24659 - Memory safe D page lacks information on return ref.
Reword `return scope` docs (before this was just listed as `return`).
Move sentence about constructor `return` attribute after method attribute.
* 'indicate' grammar
Co-authored-by: Dennis <dkorpel@users.noreply.github.com>
* `this` is considered the first parameter
* `return` can't appear after free function parameter list
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Co-authored-by: Dennis <dkorpel@users.noreply.github.com>