[PoC] infer scope for in with DIP1000

[rainers]

As an alternative to #10506
Differences:

• only enabled with -preview=dip1000
• parameter storage type changed in semantics, not during parsing
• scope only considered inferred, so not visible in header generation
• in emitted by __traits(getParameterStorageClasses)
• in added to mangling

[dlang-bot]

Thanks for your pull request, @rainers!

Bugzilla references

Your PR doesn't reference any Bugzilla issue.

If your PR contains non-trivial changes, please reference a Bugzilla issue or create a manual changelog.

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub fetch digger
dub run digger -- build "master + dmd#10526"

[rainers]

Updated to keep in for the parameter in __traits(getParameterStorageClasses) (needs some patch in std.traits.extractParameterStorageClassFlags) and add it to the mangling (needs dlang/druntime#2847).

[MoonlightSentinel]

Can this be closed given -preview=in?

[rainers]

I don't think the implementation of patching the code in the parser is correct, but I'm currently not planning to work on this.