Make ReflectionAttribute::newInstance() respect the strict_types=1
declaration at the attribute use-site. More generally, pretend that
we are calling the attribute constructor from the place where the
attribute is used, which also means that the attribute location will
show up properly in backtraces and inside "called in" error information.
This requires us to store the attributes strict_types scope (as flags),
as well as the attribute line number. The attribute filename can be
recovered from the symbol it is used on. We might want to expose the
attribute line number via reflection as well.
See also https://externals.io/message/111915.
Closes GH-6201.
Nikita Popov