* Add passing tests for property fetch on an @internal class
I'm trying to work out why the equivilent InvalidCodeParse test is
failing for PsalmInternal
* Treat all properties of a psalm-internal class as psalm-internal
* Remove all $internal properties from storage - use psalm_internal instead
@internal can be represented as internal to the namespace root, avoiding
the need to check for both properties in storage later.
* Raise InternalClass issue when an internal class is used with e.g. instanceOf
* fix docs and tests
* Add return type declartion to code example in doc
* Don't allow class psalm-internal to overide a tighter method psalm-internal
* Break up long line
* Code style - move && from EOL to SOL
* Restore misplaced &&
* Fix code style
* Fix namespace fetching so it works
Co-authored-by: Matthew Brown <github@muglug.com>
